//! Immediate operands for Cranelift instructions
//!
//! This module defines the types of immediate operands that can appear on Cranelift instructions.
//! Each type here should have a corresponding definition in the
//! `cranelift-codegen/meta/src/shared/immediates` crate in the meta language.

use alloc::vec::Vec;
use core::cmp::Ordering;
use core::convert::TryFrom;
use core::fmt::{self, Display, Formatter};
use core::str::FromStr;
use core::{i32, u32};
#[cfg(feature = "enable-serde")]
use serde::{Deserialize, Serialize};

/// Convert a type into a vector of bytes; all implementors in this file must use little-endian
/// orderings of bytes to match WebAssembly's little-endianness.
pub trait IntoBytes {
    /// Return the little-endian byte representation of the implementing type.
    fn into_bytes(self) -> Vec<u8>;
}

impl IntoBytes for u8 {
    fn into_bytes(self) -> Vec<u8> {
        vec![self]
    }
}

impl IntoBytes for i8 {
    fn into_bytes(self) -> Vec<u8> {
        vec![self as u8]
    }
}

impl IntoBytes for i16 {
    fn into_bytes(self) -> Vec<u8> {
        self.to_le_bytes().to_vec()
    }
}

impl IntoBytes for i32 {
    fn into_bytes(self) -> Vec<u8> {
        self.to_le_bytes().to_vec()
    }
}

impl IntoBytes for Vec<u8> {
    fn into_bytes(self) -> Vec<u8> {
        self
    }
}

/// 64-bit immediate signed integer operand.
///
/// An `Imm64` operand can also be used to represent immediate values of smaller integer types by
/// sign-extending to `i64`.
#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
pub struct Imm64(i64);

impl Imm64 {
    /// Create a new `Imm64` representing the signed number `x`.
    pub fn new(x: i64) -> Self {
        Self(x)
    }

    /// Return self negated.
    pub fn wrapping_neg(self) -> Self {
        Self(self.0.wrapping_neg())
    }

    /// Returns the value of this immediate.
    pub fn bits(&self) -> i64 {
        self.0
    }

    /// Sign extend this immediate as if it were a signed integer of the given
    /// power-of-two width.
    pub fn sign_extend_from_width(&mut self, bit_width: u32) {
        debug_assert!(bit_width.is_power_of_two());

        if bit_width >= 64 {
            return;
        }

        let bit_width = i64::from(bit_width);
        let delta = 64 - bit_width;
        let sign_extended = (self.0 << delta) >> delta;
        *self = Imm64(sign_extended);
    }
}

impl From<Imm64> for i64 {
    fn from(val: Imm64) -> i64 {
        val.0
    }
}

impl IntoBytes for Imm64 {
    fn into_bytes(self) -> Vec<u8> {
        self.0.to_le_bytes().to_vec()
    }
}

impl From<i64> for Imm64 {
    fn from(x: i64) -> Self {
        Self(x)
    }
}

impl Display for Imm64 {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        let x = self.0;
        if -10_000 < x && x < 10_000 {
            // Use decimal for small numbers.
            write!(f, "{}", x)
        } else {
            write_hex(x as u64, f)
        }
    }
}

/// Parse a 64-bit signed number.
fn parse_i64(s: &str) -> Result<i64, &'static str> {
    let negative = s.starts_with('-');
    let s2 = if negative || s.starts_with('+') {
        &s[1..]
    } else {
        s
    };

    let mut value = parse_u64(s2)?;

    // We support the range-and-a-half from -2^63 .. 2^64-1.
    if negative {
        value = value.wrapping_neg();
        // Don't allow large negative values to wrap around and become positive.
        if value as i64 > 0 {
            return Err("Negative number too small");
        }
    }
    Ok(value as i64)
}

impl FromStr for Imm64 {
    type Err = &'static str;

    // Parse a decimal or hexadecimal `Imm64`, formatted as above.
    fn from_str(s: &str) -> Result<Self, &'static str> {
        parse_i64(s).map(Self::new)
    }
}

/// 64-bit immediate unsigned integer operand.
///
/// A `Uimm64` operand can also be used to represent immediate values of smaller integer types by
/// zero-extending to `i64`.
#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
pub struct Uimm64(u64);

impl Uimm64 {
    /// Create a new `Uimm64` representing the unsigned number `x`.
    pub fn new(x: u64) -> Self {
        Self(x)
    }

    /// Return self negated.
    pub fn wrapping_neg(self) -> Self {
        Self(self.0.wrapping_neg())
    }
}

impl From<Uimm64> for u64 {
    fn from(val: Uimm64) -> u64 {
        val.0
    }
}

impl From<u64> for Uimm64 {
    fn from(x: u64) -> Self {
        Self(x)
    }
}

/// Hexadecimal with a multiple of 4 digits and group separators:
///
///   0xfff0
///   0x0001_ffff
///   0xffff_ffff_fff8_4400
///
fn write_hex(x: u64, f: &mut Formatter) -> fmt::Result {
    let mut pos = (64 - x.leading_zeros() - 1) & 0xf0;
    write!(f, "0x{:04x}", (x >> pos) & 0xffff)?;
    while pos > 0 {
        pos -= 16;
        write!(f, "_{:04x}", (x >> pos) & 0xffff)?;
    }
    Ok(())
}

impl Display for Uimm64 {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        let x = self.0;
        if x < 10_000 {
            // Use decimal for small numbers.
            write!(f, "{}", x)
        } else {
            write_hex(x, f)
        }
    }
}

/// Parse a 64-bit unsigned number.
fn parse_u64(s: &str) -> Result<u64, &'static str> {
    let mut value: u64 = 0;
    let mut digits = 0;

    if s.starts_with("-0x") {
        return Err("Invalid character in hexadecimal number");
    } else if s.starts_with("0x") {
        // Hexadecimal.
        for ch in s[2..].chars() {
            match ch.to_digit(16) {
                Some(digit) => {
                    digits += 1;
                    if digits > 16 {
                        return Err("Too many hexadecimal digits");
                    }
                    // This can't overflow given the digit limit.
                    value = (value << 4) | u64::from(digit);
                }
                None => {
                    // Allow embedded underscores, but fail on anything else.
                    if ch != '_' {
                        return Err("Invalid character in hexadecimal number");
                    }
                }
            }
        }
    } else {
        // Decimal number, possibly negative.
        for ch in s.chars() {
            match ch.to_digit(16) {
                Some(digit) => {
                    digits += 1;
                    match value.checked_mul(10) {
                        None => return Err("Too large decimal number"),
                        Some(v) => value = v,
                    }
                    match value.checked_add(u64::from(digit)) {
                        None => return Err("Too large decimal number"),
                        Some(v) => value = v,
                    }
                }
                None => {
                    // Allow embedded underscores, but fail on anything else.
                    if ch != '_' {
                        return Err("Invalid character in decimal number");
                    }
                }
            }
        }
    }

    if digits == 0 {
        return Err("No digits in number");
    }

    Ok(value)
}

impl FromStr for Uimm64 {
    type Err = &'static str;

    // Parse a decimal or hexadecimal `Uimm64`, formatted as above.
    fn from_str(s: &str) -> Result<Self, &'static str> {
        parse_u64(s).map(Self::new)
    }
}

/// 8-bit unsigned integer immediate operand.
///
/// This is used to indicate lane indexes typically.
pub type Uimm8 = u8;

/// A 32-bit unsigned integer immediate operand.
///
/// This is used to represent sizes of memory objects.
#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
pub struct Uimm32(u32);

impl From<Uimm32> for u32 {
    fn from(val: Uimm32) -> u32 {
        val.0
    }
}

impl From<Uimm32> for u64 {
    fn from(val: Uimm32) -> u64 {
        val.0.into()
    }
}

impl From<Uimm32> for i64 {
    fn from(val: Uimm32) -> i64 {
        i64::from(val.0)
    }
}

impl From<u32> for Uimm32 {
    fn from(x: u32) -> Self {
        Self(x)
    }
}

impl Display for Uimm32 {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        if self.0 < 10_000 {
            write!(f, "{}", self.0)
        } else {
            write_hex(u64::from(self.0), f)
        }
    }
}

impl FromStr for Uimm32 {
    type Err = &'static str;

    // Parse a decimal or hexadecimal `Uimm32`, formatted as above.
    fn from_str(s: &str) -> Result<Self, &'static str> {
        parse_i64(s).and_then(|x| {
            if 0 <= x && x <= i64::from(u32::MAX) {
                Ok(Self(x as u32))
            } else {
                Err("Uimm32 out of range")
            }
        })
    }
}

/// A 128-bit immediate operand.
///
/// This is used as an immediate value in SIMD instructions.
#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
pub struct V128Imm(pub [u8; 16]);

impl V128Imm {
    /// Iterate over the bytes in the constant.
    pub fn bytes(&self) -> impl Iterator<Item = &u8> {
        self.0.iter()
    }

    /// Convert the immediate into a vector.
    pub fn to_vec(self) -> Vec<u8> {
        self.0.to_vec()
    }

    /// Convert the immediate into a slice.
    pub fn as_slice(&self) -> &[u8] {
        &self.0[..]
    }
}

impl From<&[u8]> for V128Imm {
    fn from(slice: &[u8]) -> Self {
        assert_eq!(slice.len(), 16);
        let mut buffer = [0; 16];
        buffer.copy_from_slice(slice);
        Self(buffer)
    }
}

impl From<u128> for V128Imm {
    fn from(val: u128) -> Self {
        V128Imm(val.to_le_bytes())
    }
}

/// 32-bit signed immediate offset.
///
/// This is used to encode an immediate offset for load/store instructions. All supported ISAs have
/// a maximum load/store offset that fits in an `i32`.
#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
pub struct Offset32(i32);

impl Offset32 {
    /// Create a new `Offset32` representing the signed number `x`.
    pub fn new(x: i32) -> Self {
        Self(x)
    }

    /// Create a new `Offset32` representing the signed number `x` if possible.
    pub fn try_from_i64(x: i64) -> Option<Self> {
        let x = i32::try_from(x).ok()?;
        Some(Self::new(x))
    }

    /// Add in the signed number `x` if possible.
    pub fn try_add_i64(self, x: i64) -> Option<Self> {
        let x = i32::try_from(x).ok()?;
        let ret = self.0.checked_add(x)?;
        Some(Self::new(ret))
    }
}

impl From<Offset32> for i32 {
    fn from(val: Offset32) -> i32 {
        val.0
    }
}

impl From<Offset32> for i64 {
    fn from(val: Offset32) -> i64 {
        i64::from(val.0)
    }
}

impl From<i32> for Offset32 {
    fn from(x: i32) -> Self {
        Self(x)
    }
}

impl Display for Offset32 {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        // 0 displays as an empty offset.
        if self.0 == 0 {
            return Ok(());
        }

        // Always include a sign.
        write!(f, "{}", if self.0 < 0 { '-' } else { '+' })?;

        let val = i64::from(self.0).abs();
        if val < 10_000 {
            write!(f, "{}", val)
        } else {
            write_hex(val as u64, f)
        }
    }
}

impl FromStr for Offset32 {
    type Err = &'static str;

    // Parse a decimal or hexadecimal `Offset32`, formatted as above.
    fn from_str(s: &str) -> Result<Self, &'static str> {
        if !(s.starts_with('-') || s.starts_with('+')) {
            return Err("Offset must begin with sign");
        }
        parse_i64(s).and_then(|x| {
            if i64::from(i32::MIN) <= x && x <= i64::from(i32::MAX) {
                Ok(Self::new(x as i32))
            } else {
                Err("Offset out of range")
            }
        })
    }
}

/// An IEEE binary32 immediate floating point value, represented as a u32
/// containing the bit pattern.
///
/// All bit patterns are allowed.
#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
#[repr(C)]
pub struct Ieee32(u32);

/// An IEEE binary64 immediate floating point value, represented as a u64
/// containing the bit pattern.
///
/// All bit patterns are allowed.
#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
#[repr(C)]
pub struct Ieee64(u64);

/// Format a floating point number in a way that is reasonably human-readable, and that can be
/// converted back to binary without any rounding issues. The hexadecimal formatting of normal and
/// subnormal numbers is compatible with C99 and the `printf "%a"` format specifier. The NaN and Inf
/// formats are not supported by C99.
///
/// The encoding parameters are:
///
/// w - exponent field width in bits
/// t - trailing significand field width in bits
///
fn format_float(bits: u64, w: u8, t: u8, f: &mut Formatter) -> fmt::Result {
    debug_assert!(w > 0 && w <= 16, "Invalid exponent range");
    debug_assert!(1 + w + t <= 64, "Too large IEEE format for u64");
    debug_assert!((t + w + 1).is_power_of_two(), "Unexpected IEEE format size");

    let max_e_bits = (1u64 << w) - 1;
    let t_bits = bits & ((1u64 << t) - 1); // Trailing significand.
    let e_bits = (bits >> t) & max_e_bits; // Biased exponent.
    let sign_bit = (bits >> (w + t)) & 1;

    let bias: i32 = (1 << (w - 1)) - 1;
    let e = e_bits as i32 - bias; // Unbiased exponent.
    let emin = 1 - bias; // Minimum exponent.

    // How many hexadecimal digits are needed for the trailing significand?
    let digits = (t + 3) / 4;
    // Trailing significand left-aligned in `digits` hexadecimal digits.
    let left_t_bits = t_bits << (4 * digits - t);

    // All formats share the leading sign.
    if sign_bit != 0 {
        write!(f, "-")?;
    }

    if e_bits == 0 {
        if t_bits == 0 {
            // Zero.
            write!(f, "0.0")
        } else {
            // Subnormal.
            write!(
                f,
                "0x0.{0:01$x}p{2}",
                left_t_bits,
                usize::from(digits),
                emin
            )
        }
    } else if e_bits == max_e_bits {
        // Always print a `+` or `-` sign for these special values.
        // This makes them easier to parse as they can't be confused as identifiers.
        if sign_bit == 0 {
            write!(f, "+")?;
        }
        if t_bits == 0 {
            // Infinity.
            write!(f, "Inf")
        } else {
            // NaN.
            let payload = t_bits & ((1 << (t - 1)) - 1);
            if t_bits & (1 << (t - 1)) != 0 {
                // Quiet NaN.
                if payload != 0 {
                    write!(f, "NaN:0x{:x}", payload)
                } else {
                    write!(f, "NaN")
                }
            } else {
                // Signaling NaN.
                write!(f, "sNaN:0x{:x}", payload)
            }
        }
    } else {
        // Normal number.
        write!(f, "0x1.{0:01$x}p{2}", left_t_bits, usize::from(digits), e)
    }
}

/// Parse a float using the same format as `format_float` above.
///
/// The encoding parameters are:
///
/// w - exponent field width in bits
/// t - trailing significand field width in bits
///
fn parse_float(s: &str, w: u8, t: u8) -> Result<u64, &'static str> {
    debug_assert!(w > 0 && w <= 16, "Invalid exponent range");
    debug_assert!(1 + w + t <= 64, "Too large IEEE format for u64");
    debug_assert!((t + w + 1).is_power_of_two(), "Unexpected IEEE format size");

    let (sign_bit, s2) = if s.starts_with('-') {
        (1u64 << (t + w), &s[1..])
    } else if s.starts_with('+') {
        (0, &s[1..])
    } else {
        (0, s)
    };

    if !s2.starts_with("0x") {
        let max_e_bits = ((1u64 << w) - 1) << t;
        let quiet_bit = 1u64 << (t - 1);

        // The only decimal encoding allowed is 0.
        if s2 == "0.0" {
            return Ok(sign_bit);
        }

        if s2 == "Inf" {
            // +/- infinity: e = max, t = 0.
            return Ok(sign_bit | max_e_bits);
        }
        if s2 == "NaN" {
            // Canonical quiet NaN: e = max, t = quiet.
            return Ok(sign_bit | max_e_bits | quiet_bit);
        }
        if s2.starts_with("NaN:0x") {
            // Quiet NaN with payload.
            return match u64::from_str_radix(&s2[6..], 16) {
                Ok(payload) if payload < quiet_bit => {
                    Ok(sign_bit | max_e_bits | quiet_bit | payload)
                }
                _ => Err("Invalid NaN payload"),
            };
        }
        if s2.starts_with("sNaN:0x") {
            // Signaling NaN with payload.
            return match u64::from_str_radix(&s2[7..], 16) {
                Ok(payload) if 0 < payload && payload < quiet_bit => {
                    Ok(sign_bit | max_e_bits | payload)
                }
                _ => Err("Invalid sNaN payload"),
            };
        }

        return Err("Float must be hexadecimal");
    }
    let s3 = &s2[2..];

    let mut digits = 0u8;
    let mut digits_before_period: Option<u8> = None;
    let mut significand = 0u64;
    let mut exponent = 0i32;

    for (idx, ch) in s3.char_indices() {
        match ch {
            '.' => {
                // This is the radix point. There can only be one.
                if digits_before_period != None {
                    return Err("Multiple radix points");
                } else {
                    digits_before_period = Some(digits);
                }
            }
            'p' => {
                // The following exponent is a decimal number.
                let exp_str = &s3[1 + idx..];
                match exp_str.parse::<i16>() {
                    Ok(e) => {
                        exponent = i32::from(e);
                        break;
                    }
                    Err(_) => return Err("Bad exponent"),
                }
            }
            _ => match ch.to_digit(16) {
                Some(digit) => {
                    digits += 1;
                    if digits > 16 {
                        return Err("Too many digits");
                    }
                    significand = (significand << 4) | u64::from(digit);
                }
                None => return Err("Invalid character"),
            },
        }
    }

    if digits == 0 {
        return Err("No digits");
    }

    if significand == 0 {
        // This is +/- 0.0.
        return Ok(sign_bit);
    }

    // Number of bits appearing after the radix point.
    match digits_before_period {
        None => {} // No radix point present.
        Some(d) => exponent -= 4 * i32::from(digits - d),
    };

    // Normalize the significand and exponent.
    let significant_bits = (64 - significand.leading_zeros()) as u8;
    if significant_bits > t + 1 {
        let adjust = significant_bits - (t + 1);
        if significand & ((1u64 << adjust) - 1) != 0 {
            return Err("Too many significant bits");
        }
        // Adjust significand down.
        significand >>= adjust;
        exponent += i32::from(adjust);
    } else {
        let adjust = t + 1 - significant_bits;
        significand <<= adjust;
        exponent -= i32::from(adjust);
    }
    debug_assert_eq!(significand >> t, 1);

    // Trailing significand excludes the high bit.
    let t_bits = significand & ((1 << t) - 1);

    let max_exp = (1i32 << w) - 2;
    let bias: i32 = (1 << (w - 1)) - 1;
    exponent += bias + i32::from(t);

    if exponent > max_exp {
        Err("Magnitude too large")
    } else if exponent > 0 {
        // This is a normal number.
        let e_bits = (exponent as u64) << t;
        Ok(sign_bit | e_bits | t_bits)
    } else if 1 - exponent <= i32::from(t) {
        // This is a subnormal number: e = 0, t = significand bits.
        // Renormalize significand for exponent = 1.
        let adjust = 1 - exponent;
        if significand & ((1u64 << adjust) - 1) != 0 {
            Err("Subnormal underflow")
        } else {
            significand >>= adjust;
            Ok(sign_bit | significand)
        }
    } else {
        Err("Magnitude too small")
    }
}

impl Ieee32 {
    /// Create a new `Ieee32` containing the bits of `x`.
    pub fn with_bits(x: u32) -> Self {
        Self(x)
    }

    /// Create an `Ieee32` number representing `2.0^n`.
    pub fn pow2<I: Into<i32>>(n: I) -> Self {
        let n = n.into();
        let w = 8;
        let t = 23;
        let bias = (1 << (w - 1)) - 1;
        let exponent = (n + bias) as u32;
        assert!(exponent > 0, "Underflow n={}", n);
        assert!(exponent < (1 << w) + 1, "Overflow n={}", n);
        Self(exponent << t)
    }

    /// Create an `Ieee32` number representing the greatest negative value
    /// not convertable from f32 to a signed integer with width n.
    pub fn fcvt_to_sint_negative_overflow<I: Into<i32>>(n: I) -> Self {
        let n = n.into();
        debug_assert!(n < 32);
        debug_assert!(23 + 1 - n < 32);
        Self::with_bits((1u32 << (32 - 1)) | Self::pow2(n - 1).0 | (1u32 << (23 + 1 - n)))
    }

    /// Return self negated.
    pub fn neg(self) -> Self {
        Self(self.0 ^ (1 << 31))
    }

    /// Create a new `Ieee32` representing the number `x`.
    pub fn with_float(x: f32) -> Self {
        Self(x.to_bits())
    }

    /// Get the bitwise representation.
    pub fn bits(self) -> u32 {
        self.0
    }

    /// Check if the value is a NaN.
    pub fn is_nan(&self) -> bool {
        f32::from_bits(self.0).is_nan()
    }

    /// Returns the square root of self.
    pub fn sqrt(self) -> Self {
        Self::with_float(f32::from_bits(self.0).sqrt())
    }
}

impl PartialOrd for Ieee32 {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        f32::from_bits(self.0).partial_cmp(&f32::from_bits(other.0))
    }
}

impl Display for Ieee32 {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        let bits: u32 = self.0;
        format_float(u64::from(bits), 8, 23, f)
    }
}

impl FromStr for Ieee32 {
    type Err = &'static str;

    fn from_str(s: &str) -> Result<Self, &'static str> {
        match parse_float(s, 8, 23) {
            Ok(b) => Ok(Self(b as u32)),
            Err(s) => Err(s),
        }
    }
}

impl From<f32> for Ieee32 {
    fn from(x: f32) -> Self {
        Self::with_float(x)
    }
}

impl IntoBytes for Ieee32 {
    fn into_bytes(self) -> Vec<u8> {
        self.0.to_le_bytes().to_vec()
    }
}

impl Ieee64 {
    /// Create a new `Ieee64` containing the bits of `x`.
    pub fn with_bits(x: u64) -> Self {
        Self(x)
    }

    /// Create an `Ieee64` number representing `2.0^n`.
    pub fn pow2<I: Into<i64>>(n: I) -> Self {
        let n = n.into();
        let w = 11;
        let t = 52;
        let bias = (1 << (w - 1)) - 1;
        let exponent = (n + bias) as u64;
        assert!(exponent > 0, "Underflow n={}", n);
        assert!(exponent < (1 << w) + 1, "Overflow n={}", n);
        Self(exponent << t)
    }

    /// Create an `Ieee64` number representing the greatest negative value
    /// not convertable from f64 to a signed integer with width n.
    pub fn fcvt_to_sint_negative_overflow<I: Into<i64>>(n: I) -> Self {
        let n = n.into();
        debug_assert!(n < 64);
        debug_assert!(52 + 1 - n < 64);
        Self::with_bits((1u64 << (64 - 1)) | Self::pow2(n - 1).0 | (1u64 << (52 + 1 - n)))
    }

    /// Return self negated.
    pub fn neg(self) -> Self {
        Self(self.0 ^ (1 << 63))
    }

    /// Create a new `Ieee64` representing the number `x`.
    pub fn with_float(x: f64) -> Self {
        Self(x.to_bits())
    }

    /// Get the bitwise representation.
    pub fn bits(self) -> u64 {
        self.0
    }

    /// Check if the value is a NaN. For [Ieee64], this means checking that the 11 exponent bits are
    /// all set.
    pub fn is_nan(&self) -> bool {
        f64::from_bits(self.0).is_nan()
    }

    /// Returns the square root of self.
    pub fn sqrt(self) -> Self {
        Self::with_float(f64::from_bits(self.0).sqrt())
    }
}

impl PartialOrd for Ieee64 {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        f64::from_bits(self.0).partial_cmp(&f64::from_bits(other.0))
    }
}

impl Display for Ieee64 {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        let bits: u64 = self.0;
        format_float(bits, 11, 52, f)
    }
}

impl FromStr for Ieee64 {
    type Err = &'static str;

    fn from_str(s: &str) -> Result<Self, &'static str> {
        match parse_float(s, 11, 52) {
            Ok(b) => Ok(Self(b)),
            Err(s) => Err(s),
        }
    }
}

impl From<f64> for Ieee64 {
    fn from(x: f64) -> Self {
        Self::with_float(x)
    }
}

impl From<u64> for Ieee64 {
    fn from(x: u64) -> Self {
        Self::with_float(f64::from_bits(x))
    }
}

impl IntoBytes for Ieee64 {
    fn into_bytes(self) -> Vec<u8> {
        self.0.to_le_bytes().to_vec()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use alloc::string::ToString;
    use core::fmt::Display;
    use core::mem;
    use core::str::FromStr;
    use core::{f32, f64};

    #[test]
    fn format_imm64() {
        assert_eq!(Imm64(0).to_string(), "0");
        assert_eq!(Imm64(9999).to_string(), "9999");
        assert_eq!(Imm64(10000).to_string(), "0x2710");
        assert_eq!(Imm64(-9999).to_string(), "-9999");
        assert_eq!(Imm64(-10000).to_string(), "0xffff_ffff_ffff_d8f0");
        assert_eq!(Imm64(0xffff).to_string(), "0xffff");
        assert_eq!(Imm64(0x10000).to_string(), "0x0001_0000");
    }

    #[test]
    fn format_uimm64() {
        assert_eq!(Uimm64(0).to_string(), "0");
        assert_eq!(Uimm64(9999).to_string(), "9999");
        assert_eq!(Uimm64(10000).to_string(), "0x2710");
        assert_eq!(Uimm64(-9999i64 as u64).to_string(), "0xffff_ffff_ffff_d8f1");
        assert_eq!(
            Uimm64(-10000i64 as u64).to_string(),
            "0xffff_ffff_ffff_d8f0"
        );
        assert_eq!(Uimm64(0xffff).to_string(), "0xffff");
        assert_eq!(Uimm64(0x10000).to_string(), "0x0001_0000");
    }

    // Verify that `text` can be parsed as a `T` into a value that displays as `want`.
    fn parse_ok<T: FromStr + Display>(text: &str, want: &str)
    where
        <T as FromStr>::Err: Display,
    {
        match text.parse::<T>() {
            Err(s) => panic!("\"{}\".parse() error: {}", text, s),
            Ok(x) => assert_eq!(x.to_string(), want),
        }
    }

    // Verify that `text` fails to parse as `T` with the error `msg`.
    fn parse_err<T: FromStr + Display>(text: &str, msg: &str)
    where
        <T as FromStr>::Err: Display,
    {
        match text.parse::<T>() {
            Err(s) => assert_eq!(s.to_string(), msg),
            Ok(x) => panic!("Wanted Err({}), but got {}", msg, x),
        }
    }

    #[test]
    fn parse_imm64() {
        parse_ok::<Imm64>("0", "0");
        parse_ok::<Imm64>("1", "1");
        parse_ok::<Imm64>("-0", "0");
        parse_ok::<Imm64>("-1", "-1");
        parse_ok::<Imm64>("0x0", "0");
        parse_ok::<Imm64>("0xf", "15");
        parse_ok::<Imm64>("-0x9", "-9");

        // Probe limits.
        parse_ok::<Imm64>("0xffffffff_ffffffff", "-1");
        parse_ok::<Imm64>("0x80000000_00000000", "0x8000_0000_0000_0000");
        parse_ok::<Imm64>("-0x80000000_00000000", "0x8000_0000_0000_0000");
        parse_err::<Imm64>("-0x80000000_00000001", "Negative number too small");
        parse_ok::<Imm64>("18446744073709551615", "-1");
        parse_ok::<Imm64>("-9223372036854775808", "0x8000_0000_0000_0000");
        // Overflow both the `checked_add` and `checked_mul`.
        parse_err::<Imm64>("18446744073709551616", "Too large decimal number");
        parse_err::<Imm64>("184467440737095516100", "Too large decimal number");
        parse_err::<Imm64>("-9223372036854775809", "Negative number too small");

        // Underscores are allowed where digits go.
        parse_ok::<Imm64>("0_0", "0");
        parse_ok::<Imm64>("-_10_0", "-100");
        parse_ok::<Imm64>("_10_", "10");
        parse_ok::<Imm64>("0x97_88_bb", "0x0097_88bb");
        parse_ok::<Imm64>("0x_97_", "151");

        parse_err::<Imm64>("", "No digits in number");
        parse_err::<Imm64>("-", "No digits in number");
        parse_err::<Imm64>("_", "No digits in number");
        parse_err::<Imm64>("0x", "No digits in number");
        parse_err::<Imm64>("0x_", "No digits in number");
        parse_err::<Imm64>("-0x", "No digits in number");
        parse_err::<Imm64>(" ", "Invalid character in decimal number");
        parse_err::<Imm64>("0 ", "Invalid character in decimal number");
        parse_err::<Imm64>(" 0", "Invalid character in decimal number");
        parse_err::<Imm64>("--", "Invalid character in decimal number");
        parse_err::<Imm64>("-0x-", "Invalid character in hexadecimal number");

        // Hex count overflow.
        parse_err::<Imm64>("0x0_0000_0000_0000_0000", "Too many hexadecimal digits");
    }

    #[test]
    fn parse_uimm64() {
        parse_ok::<Uimm64>("0", "0");
        parse_ok::<Uimm64>("1", "1");
        parse_ok::<Uimm64>("0x0", "0");
        parse_ok::<Uimm64>("0xf", "15");
        parse_ok::<Uimm64>("0xffffffff_fffffff7", "0xffff_ffff_ffff_fff7");

        // Probe limits.
        parse_ok::<Uimm64>("0xffffffff_ffffffff", "0xffff_ffff_ffff_ffff");
        parse_ok::<Uimm64>("0x80000000_00000000", "0x8000_0000_0000_0000");
        parse_ok::<Uimm64>("18446744073709551615", "0xffff_ffff_ffff_ffff");
        // Overflow both the `checked_add` and `checked_mul`.
        parse_err::<Uimm64>("18446744073709551616", "Too large decimal number");
        parse_err::<Uimm64>("184467440737095516100", "Too large decimal number");

        // Underscores are allowed where digits go.
        parse_ok::<Uimm64>("0_0", "0");
        parse_ok::<Uimm64>("_10_", "10");
        parse_ok::<Uimm64>("0x97_88_bb", "0x0097_88bb");
        parse_ok::<Uimm64>("0x_97_", "151");

        parse_err::<Uimm64>("", "No digits in number");
        parse_err::<Uimm64>("_", "No digits in number");
        parse_err::<Uimm64>("0x", "No digits in number");
        parse_err::<Uimm64>("0x_", "No digits in number");
        parse_err::<Uimm64>("-", "Invalid character in decimal number");
        parse_err::<Uimm64>("-0x", "Invalid character in hexadecimal number");
        parse_err::<Uimm64>(" ", "Invalid character in decimal number");
        parse_err::<Uimm64>("0 ", "Invalid character in decimal number");
        parse_err::<Uimm64>(" 0", "Invalid character in decimal number");
        parse_err::<Uimm64>("--", "Invalid character in decimal number");
        parse_err::<Uimm64>("-0x-", "Invalid character in hexadecimal number");
        parse_err::<Uimm64>("-0", "Invalid character in decimal number");
        parse_err::<Uimm64>("-1", "Invalid character in decimal number");

        // Hex count overflow.
        parse_err::<Uimm64>("0x0_0000_0000_0000_0000", "Too many hexadecimal digits");
    }

    #[test]
    fn format_offset32() {
        assert_eq!(Offset32(0).to_string(), "");
        assert_eq!(Offset32(1).to_string(), "+1");
        assert_eq!(Offset32(-1).to_string(), "-1");
        assert_eq!(Offset32(9999).to_string(), "+9999");
        assert_eq!(Offset32(10000).to_string(), "+0x2710");
        assert_eq!(Offset32(-9999).to_string(), "-9999");
        assert_eq!(Offset32(-10000).to_string(), "-0x2710");
        assert_eq!(Offset32(0xffff).to_string(), "+0xffff");
        assert_eq!(Offset32(0x10000).to_string(), "+0x0001_0000");
    }

    #[test]
    fn parse_offset32() {
        parse_ok::<Offset32>("+0", "");
        parse_ok::<Offset32>("+1", "+1");
        parse_ok::<Offset32>("-0", "");
        parse_ok::<Offset32>("-1", "-1");
        parse_ok::<Offset32>("+0x0", "");
        parse_ok::<Offset32>("+0xf", "+15");
        parse_ok::<Offset32>("-0x9", "-9");
        parse_ok::<Offset32>("-0x8000_0000", "-0x8000_0000");

        parse_err::<Offset32>("+0x8000_0000", "Offset out of range");
    }

    #[test]
    fn format_ieee32() {
        assert_eq!(Ieee32::with_float(0.0).to_string(), "0.0");
        assert_eq!(Ieee32::with_float(-0.0).to_string(), "-0.0");
        assert_eq!(Ieee32::with_float(1.0).to_string(), "0x1.000000p0");
        assert_eq!(Ieee32::with_float(1.5).to_string(), "0x1.800000p0");
        assert_eq!(Ieee32::with_float(0.5).to_string(), "0x1.000000p-1");
        assert_eq!(
            Ieee32::with_float(f32::EPSILON).to_string(),
            "0x1.000000p-23"
        );
        assert_eq!(Ieee32::with_float(f32::MIN).to_string(), "-0x1.fffffep127");
        assert_eq!(Ieee32::with_float(f32::MAX).to_string(), "0x1.fffffep127");
        // Smallest positive normal number.
        assert_eq!(
            Ieee32::with_float(f32::MIN_POSITIVE).to_string(),
            "0x1.000000p-126"
        );
        // Subnormals.
        assert_eq!(
            Ieee32::with_float(f32::MIN_POSITIVE / 2.0).to_string(),
            "0x0.800000p-126"
        );
        assert_eq!(
            Ieee32::with_float(f32::MIN_POSITIVE * f32::EPSILON).to_string(),
            "0x0.000002p-126"
        );
        assert_eq!(Ieee32::with_float(f32::INFINITY).to_string(), "+Inf");
        assert_eq!(Ieee32::with_float(f32::NEG_INFINITY).to_string(), "-Inf");
        assert_eq!(Ieee32::with_float(f32::NAN).to_string(), "+NaN");
        assert_eq!(Ieee32::with_float(-f32::NAN).to_string(), "-NaN");
        // Construct some qNaNs with payloads.
        assert_eq!(Ieee32(0x7fc00001).to_string(), "+NaN:0x1");
        assert_eq!(Ieee32(0x7ff00001).to_string(), "+NaN:0x300001");
        // Signaling NaNs.
        assert_eq!(Ieee32(0x7f800001).to_string(), "+sNaN:0x1");
        assert_eq!(Ieee32(0x7fa00001).to_string(), "+sNaN:0x200001");
    }

    #[test]
    fn parse_ieee32() {
        parse_ok::<Ieee32>("0.0", "0.0");
        parse_ok::<Ieee32>("+0.0", "0.0");
        parse_ok::<Ieee32>("-0.0", "-0.0");
        parse_ok::<Ieee32>("0x0", "0.0");
        parse_ok::<Ieee32>("0x0.0", "0.0");
        parse_ok::<Ieee32>("0x.0", "0.0");
        parse_ok::<Ieee32>("0x0.", "0.0");
        parse_ok::<Ieee32>("0x1", "0x1.000000p0");
        parse_ok::<Ieee32>("+0x1", "0x1.000000p0");
        parse_ok::<Ieee32>("-0x1", "-0x1.000000p0");
        parse_ok::<Ieee32>("0x10", "0x1.000000p4");
        parse_ok::<Ieee32>("0x10.0", "0x1.000000p4");
        parse_err::<Ieee32>("0.", "Float must be hexadecimal");
        parse_err::<Ieee32>(".0", "Float must be hexadecimal");
        parse_err::<Ieee32>("0", "Float must be hexadecimal");
        parse_err::<Ieee32>("-0", "Float must be hexadecimal");
        parse_err::<Ieee32>(".", "Float must be hexadecimal");
        parse_err::<Ieee32>("", "Float must be hexadecimal");
        parse_err::<Ieee32>("-", "Float must be hexadecimal");
        parse_err::<Ieee32>("0x", "No digits");
        parse_err::<Ieee32>("0x..", "Multiple radix points");

        // Check significant bits.
        parse_ok::<Ieee32>("0x0.ffffff", "0x1.fffffep-1");
        parse_ok::<Ieee32>("0x1.fffffe", "0x1.fffffep0");
        parse_ok::<Ieee32>("0x3.fffffc", "0x1.fffffep1");
        parse_ok::<Ieee32>("0x7.fffff8", "0x1.fffffep2");
        parse_ok::<Ieee32>("0xf.fffff0", "0x1.fffffep3");
        parse_err::<Ieee32>("0x1.ffffff", "Too many significant bits");
        parse_err::<Ieee32>("0x1.fffffe0000000000", "Too many digits");

        // Exponents.
        parse_ok::<Ieee32>("0x1p3", "0x1.000000p3");
        parse_ok::<Ieee32>("0x1p-3", "0x1.000000p-3");
        parse_ok::<Ieee32>("0x1.0p3", "0x1.000000p3");
        parse_ok::<Ieee32>("0x2.0p3", "0x1.000000p4");
        parse_ok::<Ieee32>("0x1.0p127", "0x1.000000p127");
        parse_ok::<Ieee32>("0x1.0p-126", "0x1.000000p-126");
        parse_ok::<Ieee32>("0x0.1p-122", "0x1.000000p-126");
        parse_err::<Ieee32>("0x2.0p127", "Magnitude too large");

        // Subnormals.
        parse_ok::<Ieee32>("0x1.0p-127", "0x0.800000p-126");
        parse_ok::<Ieee32>("0x1.0p-149", "0x0.000002p-126");
        parse_ok::<Ieee32>("0x0.000002p-126", "0x0.000002p-126");
        parse_err::<Ieee32>("0x0.100001p-126", "Subnormal underflow");
        parse_err::<Ieee32>("0x1.8p-149", "Subnormal underflow");
        parse_err::<Ieee32>("0x1.0p-150", "Magnitude too small");

        // NaNs and Infs.
        parse_ok::<Ieee32>("Inf", "+Inf");
        parse_ok::<Ieee32>("+Inf", "+Inf");
        parse_ok::<Ieee32>("-Inf", "-Inf");
        parse_ok::<Ieee32>("NaN", "+NaN");
        parse_ok::<Ieee32>("+NaN", "+NaN");
        parse_ok::<Ieee32>("-NaN", "-NaN");
        parse_ok::<Ieee32>("NaN:0x0", "+NaN");
        parse_err::<Ieee32>("NaN:", "Float must be hexadecimal");
        parse_err::<Ieee32>("NaN:0", "Float must be hexadecimal");
        parse_err::<Ieee32>("NaN:0x", "Invalid NaN payload");
        parse_ok::<Ieee32>("NaN:0x000001", "+NaN:0x1");
        parse_ok::<Ieee32>("NaN:0x300001", "+NaN:0x300001");
        parse_err::<Ieee32>("NaN:0x400001", "Invalid NaN payload");
        parse_ok::<Ieee32>("sNaN:0x1", "+sNaN:0x1");
        parse_err::<Ieee32>("sNaN:0x0", "Invalid sNaN payload");
        parse_ok::<Ieee32>("sNaN:0x200001", "+sNaN:0x200001");
        parse_err::<Ieee32>("sNaN:0x400001", "Invalid sNaN payload");
    }

    #[test]
    fn pow2_ieee32() {
        assert_eq!(Ieee32::pow2(0).to_string(), "0x1.000000p0");
        assert_eq!(Ieee32::pow2(1).to_string(), "0x1.000000p1");
        assert_eq!(Ieee32::pow2(-1).to_string(), "0x1.000000p-1");
        assert_eq!(Ieee32::pow2(127).to_string(), "0x1.000000p127");
        assert_eq!(Ieee32::pow2(-126).to_string(), "0x1.000000p-126");

        assert_eq!(Ieee32::pow2(1).neg().to_string(), "-0x1.000000p1");
    }

    #[test]
    fn fcvt_to_sint_negative_overflow_ieee32() {
        for n in &[8, 16] {
            assert_eq!(-((1u32 << (n - 1)) as f32) - 1.0, unsafe {
                mem::transmute(Ieee32::fcvt_to_sint_negative_overflow(*n))
            });
        }
    }

    #[test]
    fn format_ieee64() {
        assert_eq!(Ieee64::with_float(0.0).to_string(), "0.0");
        assert_eq!(Ieee64::with_float(-0.0).to_string(), "-0.0");
        assert_eq!(Ieee64::with_float(1.0).to_string(), "0x1.0000000000000p0");
        assert_eq!(Ieee64::with_float(1.5).to_string(), "0x1.8000000000000p0");
        assert_eq!(Ieee64::with_float(0.5).to_string(), "0x1.0000000000000p-1");
        assert_eq!(
            Ieee64::with_float(f64::EPSILON).to_string(),
            "0x1.0000000000000p-52"
        );
        assert_eq!(
            Ieee64::with_float(f64::MIN).to_string(),
            "-0x1.fffffffffffffp1023"
        );
        assert_eq!(
            Ieee64::with_float(f64::MAX).to_string(),
            "0x1.fffffffffffffp1023"
        );
        // Smallest positive normal number.
        assert_eq!(
            Ieee64::with_float(f64::MIN_POSITIVE).to_string(),
            "0x1.0000000000000p-1022"
        );
        // Subnormals.
        assert_eq!(
            Ieee64::with_float(f64::MIN_POSITIVE / 2.0).to_string(),
            "0x0.8000000000000p-1022"
        );
        assert_eq!(
            Ieee64::with_float(f64::MIN_POSITIVE * f64::EPSILON).to_string(),
            "0x0.0000000000001p-1022"
        );
        assert_eq!(Ieee64::with_float(f64::INFINITY).to_string(), "+Inf");
        assert_eq!(Ieee64::with_float(f64::NEG_INFINITY).to_string(), "-Inf");
        assert_eq!(Ieee64::with_float(f64::NAN).to_string(), "+NaN");
        assert_eq!(Ieee64::with_float(-f64::NAN).to_string(), "-NaN");
        // Construct some qNaNs with payloads.
        assert_eq!(Ieee64(0x7ff8000000000001).to_string(), "+NaN:0x1");
        assert_eq!(
            Ieee64(0x7ffc000000000001).to_string(),
            "+NaN:0x4000000000001"
        );
        // Signaling NaNs.
        assert_eq!(Ieee64(0x7ff0000000000001).to_string(), "+sNaN:0x1");
        assert_eq!(
            Ieee64(0x7ff4000000000001).to_string(),
            "+sNaN:0x4000000000001"
        );
    }

    #[test]
    fn parse_ieee64() {
        parse_ok::<Ieee64>("0.0", "0.0");
        parse_ok::<Ieee64>("-0.0", "-0.0");
        parse_ok::<Ieee64>("0x0", "0.0");
        parse_ok::<Ieee64>("0x0.0", "0.0");
        parse_ok::<Ieee64>("0x.0", "0.0");
        parse_ok::<Ieee64>("0x0.", "0.0");
        parse_ok::<Ieee64>("0x1", "0x1.0000000000000p0");
        parse_ok::<Ieee64>("-0x1", "-0x1.0000000000000p0");
        parse_ok::<Ieee64>("0x10", "0x1.0000000000000p4");
        parse_ok::<Ieee64>("0x10.0", "0x1.0000000000000p4");
        parse_err::<Ieee64>("0.", "Float must be hexadecimal");
        parse_err::<Ieee64>(".0", "Float must be hexadecimal");
        parse_err::<Ieee64>("0", "Float must be hexadecimal");
        parse_err::<Ieee64>("-0", "Float must be hexadecimal");
        parse_err::<Ieee64>(".", "Float must be hexadecimal");
        parse_err::<Ieee64>("", "Float must be hexadecimal");
        parse_err::<Ieee64>("-", "Float must be hexadecimal");
        parse_err::<Ieee64>("0x", "No digits");
        parse_err::<Ieee64>("0x..", "Multiple radix points");

        // Check significant bits.
        parse_ok::<Ieee64>("0x0.fffffffffffff8", "0x1.fffffffffffffp-1");
        parse_ok::<Ieee64>("0x1.fffffffffffff", "0x1.fffffffffffffp0");
        parse_ok::<Ieee64>("0x3.ffffffffffffe", "0x1.fffffffffffffp1");
        parse_ok::<Ieee64>("0x7.ffffffffffffc", "0x1.fffffffffffffp2");
        parse_ok::<Ieee64>("0xf.ffffffffffff8", "0x1.fffffffffffffp3");
        parse_err::<Ieee64>("0x3.fffffffffffff", "Too many significant bits");
        parse_err::<Ieee64>("0x001.fffffe00000000", "Too many digits");

        // Exponents.
        parse_ok::<Ieee64>("0x1p3", "0x1.0000000000000p3");
        parse_ok::<Ieee64>("0x1p-3", "0x1.0000000000000p-3");
        parse_ok::<Ieee64>("0x1.0p3", "0x1.0000000000000p3");
        parse_ok::<Ieee64>("0x2.0p3", "0x1.0000000000000p4");
        parse_ok::<Ieee64>("0x1.0p1023", "0x1.0000000000000p1023");
        parse_ok::<Ieee64>("0x1.0p-1022", "0x1.0000000000000p-1022");
        parse_ok::<Ieee64>("0x0.1p-1018", "0x1.0000000000000p-1022");
        parse_err::<Ieee64>("0x2.0p1023", "Magnitude too large");

        // Subnormals.
        parse_ok::<Ieee64>("0x1.0p-1023", "0x0.8000000000000p-1022");
        parse_ok::<Ieee64>("0x1.0p-1074", "0x0.0000000000001p-1022");
        parse_ok::<Ieee64>("0x0.0000000000001p-1022", "0x0.0000000000001p-1022");
        parse_err::<Ieee64>("0x0.10000000000008p-1022", "Subnormal underflow");
        parse_err::<Ieee64>("0x1.8p-1074", "Subnormal underflow");
        parse_err::<Ieee64>("0x1.0p-1075", "Magnitude too small");

        // NaNs and Infs.
        parse_ok::<Ieee64>("Inf", "+Inf");
        parse_ok::<Ieee64>("-Inf", "-Inf");
        parse_ok::<Ieee64>("NaN", "+NaN");
        parse_ok::<Ieee64>("-NaN", "-NaN");
        parse_ok::<Ieee64>("NaN:0x0", "+NaN");
        parse_err::<Ieee64>("NaN:", "Float must be hexadecimal");
        parse_err::<Ieee64>("NaN:0", "Float must be hexadecimal");
        parse_err::<Ieee64>("NaN:0x", "Invalid NaN payload");
        parse_ok::<Ieee64>("NaN:0x000001", "+NaN:0x1");
        parse_ok::<Ieee64>("NaN:0x4000000000001", "+NaN:0x4000000000001");
        parse_err::<Ieee64>("NaN:0x8000000000001", "Invalid NaN payload");
        parse_ok::<Ieee64>("sNaN:0x1", "+sNaN:0x1");
        parse_err::<Ieee64>("sNaN:0x0", "Invalid sNaN payload");
        parse_ok::<Ieee64>("sNaN:0x4000000000001", "+sNaN:0x4000000000001");
        parse_err::<Ieee64>("sNaN:0x8000000000001", "Invalid sNaN payload");
    }

    #[test]
    fn pow2_ieee64() {
        assert_eq!(Ieee64::pow2(0).to_string(), "0x1.0000000000000p0");
        assert_eq!(Ieee64::pow2(1).to_string(), "0x1.0000000000000p1");
        assert_eq!(Ieee64::pow2(-1).to_string(), "0x1.0000000000000p-1");
        assert_eq!(Ieee64::pow2(1023).to_string(), "0x1.0000000000000p1023");
        assert_eq!(Ieee64::pow2(-1022).to_string(), "0x1.0000000000000p-1022");

        assert_eq!(Ieee64::pow2(1).neg().to_string(), "-0x1.0000000000000p1");
    }

    #[test]
    fn fcvt_to_sint_negative_overflow_ieee64() {
        for n in &[8, 16, 32] {
            assert_eq!(-((1u64 << (n - 1)) as f64) - 1.0, unsafe {
                mem::transmute(Ieee64::fcvt_to_sint_negative_overflow(*n))
            });
        }
    }
}