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Rewrite range checks in float ToPrimitive macros

This commit is contained in:
Josh Stone 2018-03-10 23:01:30 -08:00
parent 8e27c7327d
commit b025c273c7
1 changed files with 40 additions and 23 deletions
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63
src/cast.rs
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@ -1,3 +1,6 @@
use core::{i8, i16, i32, i64, isize};
use core::{u8, u16, u32, u64, usize};
use core::{f32, f64};
use core::mem::size_of; use core::mem::size_of;
use core::num::Wrapping; use core::num::Wrapping;
@ -220,43 +223,57 @@ impl_to_primitive_uint!(u32);
impl_to_primitive_uint!(u64); impl_to_primitive_uint!(u64);
macro_rules! impl_to_primitive_float_to_float { macro_rules! impl_to_primitive_float_to_float {
($SrcT:ident, $DstT:ident, $slf:expr) => ( ($SrcT:ident, $DstT:ident, $slf:expr) => ({
if size_of::<$SrcT>() <= size_of::<$DstT>() { // Only finite values that are reducing size need to worry about overflow.
Some($slf as $DstT) if size_of::<$SrcT>() > size_of::<$DstT>() && FloatCore::is_finite($slf) {
} else {
// Make sure the value is in range for the cast.
// NaN and +-inf are cast as they are.
let n = $slf as f64; let n = $slf as f64;
let max_value: $DstT = ::core::$DstT::MAX; if n < $DstT::MIN as f64 || n > $DstT::MAX as f64 {
if !FloatCore::is_finite(n) || (-max_value as f64 <= n && n <= max_value as f64) return None;
{
Some($slf as $DstT)
} else {
None
} }
} }
) // We can safely cast NaN, +-inf, and finite values in range.
Some($slf as $DstT)
})
} }
macro_rules! impl_to_primitive_float_to_signed_int { macro_rules! impl_to_primitive_float_to_signed_int {
($SrcT:ident, $DstT:ident, $slf:expr) => ({ ($SrcT:ident, $DstT:ident, $slf:expr) => ({
let t = $slf.trunc(); let t = $slf.trunc(); // round toward zero.
if t >= $DstT::min_value() as $SrcT && t <= $DstT::max_value() as $SrcT { // MIN is a power of two, which we can cast and compare directly.
Some($slf as $DstT) if t >= $DstT::MIN as $SrcT {
} else { // The mantissa might not be able to represent all digits of MAX.
None let sig_bits = size_of::<$DstT>() as u32 * 8 - 1;
let max = if sig_bits > $SrcT::MANTISSA_DIGITS {
let lost_bits = sig_bits - $SrcT::MANTISSA_DIGITS;
$DstT::MAX & !((1 << lost_bits) - 1)
} else {
$DstT::MAX
};
if t <= max as $SrcT {
return Some($slf as $DstT);
}
} }
None
}) })
} }
macro_rules! impl_to_primitive_float_to_unsigned_int { macro_rules! impl_to_primitive_float_to_unsigned_int {
($SrcT:ident, $DstT:ident, $slf:expr) => ({ ($SrcT:ident, $DstT:ident, $slf:expr) => ({
let t = $slf.trunc(); let t = $slf.trunc(); // round toward zero.
if t >= $DstT::min_value() as $SrcT && t <= $DstT::max_value() as $SrcT { if t >= 0.0 {
Some($slf as $DstT) // The mantissa might not be able to represent all digits of MAX.
} else { let sig_bits = size_of::<$DstT>() as u32 * 8;
None let max = if sig_bits > $SrcT::MANTISSA_DIGITS {
let lost_bits = sig_bits - $SrcT::MANTISSA_DIGITS;
$DstT::MAX & !((1 << lost_bits) - 1)
} else {
$DstT::MAX
};
if t <= max as $SrcT {
return Some($slf as $DstT);
}
} }
None
}) })
} }