87 lines · c
1//===-- Implementation header for rsqrtf16 ----------------------*- C++ -*-===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef LLVM_LIBC_SRC___SUPPORT_MATH_RSQRTF16_H10#define LLVM_LIBC_SRC___SUPPORT_MATH_RSQRTF16_H11 12#include "include/llvm-libc-macros/float16-macros.h"13 14#ifdef LIBC_TYPES_HAS_FLOAT1615 16#include "src/__support/FPUtil/FEnvImpl.h"17#include "src/__support/FPUtil/FPBits.h"18#include "src/__support/FPUtil/ManipulationFunctions.h"19#include "src/__support/FPUtil/cast.h"20#include "src/__support/FPUtil/multiply_add.h"21#include "src/__support/FPUtil/sqrt.h"22#include "src/__support/macros/optimization.h"23 24namespace LIBC_NAMESPACE_DECL {25namespace math {26 27LIBC_INLINE static constexpr float16 rsqrtf16(float16 x) {28 using FPBits = fputil::FPBits<float16>;29 FPBits xbits(x);30 31 uint16_t x_u = xbits.uintval();32 uint16_t x_abs = x_u & 0x7fff;33 34 constexpr uint16_t INF_BIT = FPBits::inf().uintval();35 36 // x is 0, inf/nan, or negative.37 if (LIBC_UNLIKELY(x_u == 0 || x_u >= INF_BIT)) {38 // x is NaN39 if (x_abs > INF_BIT) {40 if (xbits.is_signaling_nan()) {41 fputil::raise_except_if_required(FE_INVALID);42 return FPBits::quiet_nan().get_val();43 }44 return x;45 }46 47 // |x| = 048 if (x_abs == 0) {49 fputil::raise_except_if_required(FE_DIVBYZERO);50 fputil::set_errno_if_required(ERANGE);51 return FPBits::inf(xbits.sign()).get_val();52 }53 54 // -inf <= x < 055 if (x_u > 0x7fff) {56 fputil::raise_except_if_required(FE_INVALID);57 fputil::set_errno_if_required(EDOM);58 return FPBits::quiet_nan().get_val();59 }60 61 // x = +inf => rsqrt(x) = 062 return FPBits::zero().get_val();63 }64 65 // TODO: add integer based implementation when LIBC_TARGET_CPU_HAS_FPU_FLOAT66 // is not defined67 float result = 1.0f / fputil::sqrt<float>(fputil::cast<float>(x));68 69 // Targeted post-corrections to ensure correct rounding in half for specific70 // mantissa patterns71 const uint16_t half_mantissa = x_abs & 0x3ff;72 if (LIBC_UNLIKELY(half_mantissa == 0x011F)) {73 result = fputil::multiply_add(result, 0x1.0p-21f, result);74 } else if (LIBC_UNLIKELY(half_mantissa == 0x0313)) {75 result = fputil::multiply_add(result, -0x1.0p-21f, result);76 }77 78 return fputil::cast<float16>(result);79}80 81} // namespace math82} // namespace LIBC_NAMESPACE_DECL83 84#endif // LIBC_TYPES_HAS_FLOAT1685 86#endif // LLVM_LIBC_SRC___SUPPORT_MATH_RSQRTF16_H87