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const_fixed_from_int implementation that works on rustc 1.44

This commit is contained in:
Trevor Spiteri 2020-09-02 12:58:28 +02:00
parent c6ea032292
commit be0fd36bf5
1 changed files with 8 additions and 21 deletions
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29
src/lib.rs
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@ -590,27 +590,14 @@ fixed! {
#[macro_export]
macro_rules! const_fixed_from_int {
($(const $NAME:ident: $Fixed:ty = $int:expr;)*) => { $(
const $NAME: $Fixed = <$Fixed>::from_bits({
let int = $int;
// 0 should work even for no integer bits.
if int == 0 {
// Use int here to clearly ensure that the type of int is the inner type.
int
} else {
// Fails to compile if int is not zero and there are no integer bits.
let one_bits = <$Fixed>::from_bits(1).to_bits() << <$Fixed>::FRAC_NBITS;
if one_bits > 0 {
// one_bits is positive: multiplication overflows if int does not fit.
int * one_bits
} else if !int == 0 {
// one_bits is negative minimum for signed inner type and int is -1.
one_bits
} else {
// one_bits is negative minimum and int is not 0 or -1: overflow.
1 / 0
}
}
});
const $NAME: $Fixed = {
const FRAC: u32 = <$Fixed>::FRAC_NBITS;
// Divide shift into two parts for cases where $Fixed cannot represent 1.
// Use $Fixed as type because there isn't a const way to get the inner type.
const ONE_A: $Fixed = <$Fixed>::from_bits(1 << FRAC / 2);
const ONE_B: $Fixed = <$Fixed>::from_bits(1 << FRAC - FRAC / 2);
<$Fixed>::from_bits($int * ONE_A.to_bits() * ONE_B.to_bits())
};
)* };
}