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s390x: document the different rounding flavors #1869

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Jul 15, 2025
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s390x: document the different rounding flavors #1869

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17 changes: 14 additions & 3 deletions crates/core_arch/src/s390x/vector.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1181,6 +1181,20 @@ mod sealed {

impl_vec_trait! { [VectorOrc vec_orc]+ 2c (orc) }

// Z vector intrinsic C23 math.h LLVM IR ISO/IEC 60559 operation inexact vfidb parameters
//
// vec_rint rint llvm.rint roundToIntegralExact yes 0, 0
// vec_roundc nearbyint llvm.nearbyint n/a no 4, 0
// vec_floor / vec_roundm floor llvm.floor roundToIntegralTowardNegative no 4, 7
// vec_ceil / vec_roundp ceil llvm.ceil roundToIntegralTowardPositive no 4, 6
// vec_trunc / vec_roundz trunc llvm.trunc roundToIntegralTowardZero no 4, 5
// vec_round roundeven llvm.roundeven roundToIntegralTiesToEven no 4, 4
// n/a round llvm.round roundToIntegralTiesAway no 4, 1

// `simd_round_ties_even` is implemented as `llvm.rint`.
test_impl! { vec_rint_f32 (a: vector_float) -> vector_float [simd_round_ties_even, "vector-enhancements-1" vfisb] }
test_impl! { vec_rint_f64 (a: vector_double) -> vector_double [simd_round_ties_even, vfidb] }

test_impl! { vec_roundc_f32 (a: vector_float) -> vector_float [nearbyint_v4f32, "vector-enhancements-1" vfisb] }
test_impl! { vec_roundc_f64 (a: vector_double) -> vector_double [nearbyint_v2f64, vfidb] }

Expand All @@ -1189,9 +1203,6 @@ mod sealed {
test_impl! { vec_round_f32 (a: vector_float) -> vector_float [roundeven_v4f32, _] }
test_impl! { vec_round_f64 (a: vector_double) -> vector_double [roundeven_v2f64, _] }

test_impl! { vec_rint_f32 (a: vector_float) -> vector_float [simd_round_ties_even, "vector-enhancements-1" vfisb] }
test_impl! { vec_rint_f64 (a: vector_double) -> vector_double [simd_round_ties_even, vfidb] }

#[unstable(feature = "stdarch_s390x", issue = "135681")]
pub trait VectorRoundc {
unsafe fn vec_roundc(self) -> Self;
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