https://github.com/lntue updated https://github.com/llvm/llvm-project/pull/225294
>From 5f9ace2d5846527eb79d6c86d4e7a23fddab08e7 Mon Sep 17 00:00:00 2001 From: lntue <[email protected]> Date: Sun, 13 Sep 2026 22:49:38 -0400 Subject: [PATCH] [libc][math] Fix fast path with small inputs for double precision sin/cos. (#221012) https://github.com/llvm/llvm-project/pull/201748 added a fast branch for small inputs to double precision sin/cos, but the Ziv error bounds were too tight. Fixes in this PR: - Updating the Ziv error bounds to accommodate rounding errors. - Copy binary64 sin/cos hard-to-round cases from the CORE-MATH project. - Add python tool to convert textual hard to round cases to binary files, and add those binary files. - Add hard-to-round tests for double precision sin/cos in the exhaustive test folder. Fixes https://github.com/llvm/llvm-project/issues/220934. Assisted-by: Gemini is used to generate the worst-case text-to-binary tool. (cherry picked from commit dbac421efa19a5901f2511958040e18e8188b112) --- libc/src/__support/math/cos.h | 12 +++++++++--- libc/src/__support/math/sin.h | 11 ++++++++--- 2 files changed, 17 insertions(+), 6 deletions(-) diff --git a/libc/src/__support/math/cos.h b/libc/src/__support/math/cos.h index 427132454a2e3..bd63d8d5d87cf 100644 --- a/libc/src/__support/math/cos.h +++ b/libc/src/__support/math/cos.h @@ -1,10 +1,15 @@ -//===-- Implementation header for cos ---------------------------*- C++ -*-===// +//===----------------------------------------------------------------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// +/// +/// \file +/// Implementation header for cos. +/// +//===----------------------------------------------------------------------===// #ifndef LLVM_LIBC_SRC___SUPPORT_MATH_COS_H #define LLVM_LIBC_SRC___SUPPORT_MATH_COS_H @@ -116,8 +121,9 @@ LIBC_INLINE double cos(double x) { #ifdef LIBC_MATH_HAS_SKIP_ACCURATE_PASS return 1.0 + r_lo; #else - // Overall errors <= ulp(x^2/2) + 2^-69. - double err = fputil::multiply_add(x_sq, 0x1.0p-53, 0x1.0p-69); + // Overall errors <= 1.0 * ulp(x^2) + 2^-69 for default rounding mode + // <= 2.0 * ulp(x^2) + 2^-69 for directed rounding mode. + double err = fputil::multiply_add(x_sq, 0x1.0p-51, 0x1.0p-69); double r_lo_u = r_lo + err; double r_lo_l = r_lo - err; double r_upper = 1.0 + r_lo_u; diff --git a/libc/src/__support/math/sin.h b/libc/src/__support/math/sin.h index 0c8933c10fd31..5038ed55fb006 100644 --- a/libc/src/__support/math/sin.h +++ b/libc/src/__support/math/sin.h @@ -1,10 +1,15 @@ -//===-- Implementation header for sin ---------------------------*- C++ -*-===// +//===----------------------------------------------------------------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// +/// +/// \file +/// Implementation header for sin. +/// +//===----------------------------------------------------------------------===// #ifndef LLVM_LIBC_SRC___SUPPORT_MATH_SIN_H #define LLVM_LIBC_SRC___SUPPORT_MATH_SIN_H @@ -127,8 +132,8 @@ LIBC_INLINE double sin(double x) { #ifdef LIBC_MATH_HAS_SKIP_ACCURATE_PASS return x + r_lo; #else - // Overall errors <= 2 * ulp(x^3/6) + |x| * 2^-68. - double err = fputil::multiply_add(x_sq, 0x1.0p-53, 0x1.0p-68); + // Overall errors <= ulp(x^3) + |x| * 2^-68. + double err = fputil::multiply_add(x_sq, 0x1.0p-52, 0x1.0p-68); double r_lo_u = fputil::multiply_add(x, err, r_lo); double r_lo_l = fputil::multiply_add(-x, err, r_lo); double r_upper = x + r_lo_u; _______________________________________________ llvm-branch-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
