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Use the trifecta div algorithm for 128-bit div on wasm #685

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Sep 5, 2024
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Use the trifecta div algorithm for 128-bit div on wasm #685

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20 changes: 15 additions & 5 deletions src/int/specialized_div_rem/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -136,9 +136,15 @@ fn u64_by_u64_div_rem(duo: u64, div: u64) -> (u64, u64) {

// Whether `trifecta` or `delegate` is faster for 128 bit division depends on the speed at which a
// microarchitecture can multiply and divide. We decide to be optimistic and assume `trifecta` is
// faster if the target pointer width is at least 64.
// faster if the target pointer width is at least 64. Note that this
// implementation is additionally included on WebAssembly despite the typical
// pointer width there being 32 because it's typically run on a 64-bit machine
// that has access to faster 64-bit operations.
#[cfg(all(
not(any(target_pointer_width = "16", target_pointer_width = "32")),
any(
target_family = "wasm",
not(any(target_pointer_width = "16", target_pointer_width = "32")),
),
not(all(not(feature = "no-asm"), target_arch = "x86_64")),
not(any(target_arch = "sparc", target_arch = "sparc64"))
))]
Expand All @@ -152,10 +158,14 @@ impl_trifecta!(
u128
);

// If the pointer width less than 64, then the target architecture almost certainly does not have
// the fast 64 to 128 bit widening multiplication needed for `trifecta` to be faster.
// If the pointer width less than 64 and this isn't wasm, then the target
// architecture almost certainly does not have the fast 64 to 128 bit widening
// multiplication needed for `trifecta` to be faster.
#[cfg(all(
any(target_pointer_width = "16", target_pointer_width = "32"),
not(any(
target_family = "wasm",
not(any(target_pointer_width = "16", target_pointer_width = "32")),
)),
not(all(not(feature = "no-asm"), target_arch = "x86_64")),
not(any(target_arch = "sparc", target_arch = "sparc64"))
))]
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