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//===-- Fast rounding to nearest integer for floating point -----*- 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
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_LIBC_SRC_SUPPORT_FPUTIL_NEAREST_INTEGER_H
#define LLVM_LIBC_SRC_SUPPORT_FPUTIL_NEAREST_INTEGER_H
#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
#include "src/__support/macros/properties/architectures.h"
#include "src/__support/macros/properties/cpu_features.h"
#if (defined(LIBC_TARGET_ARCH_IS_X86_64) && defined(LIBC_TARGET_CPU_HAS_SSE4_2))
#include "x86_64/nearest_integer.h"
#elif defined(LIBC_TARGET_ARCH_IS_AARCH64)
#include "aarch64/nearest_integer.h"
#else
namespace __llvm_libc {
namespace fputil {
// This is a fast implementation for rounding to a nearest integer that.
//
// Notice that for AARCH64 and x86-64 with SSE4.2 support, we will use their
// corresponding rounding instruction instead. And in those cases, the results
// are rounded to the nearest integer, tie-to-even.
LIBC_INLINE float nearest_integer(float x) {
if (x < 0x1p24f && x > -0x1p24f) {
float r = x < 0 ? (x - 0x1.0p23f) + 0x1.0p23f : (x + 0x1.0p23f) - 0x1.0p23f;
float diff = x - r;
// The expression above is correct for the default rounding mode, round-to-
// nearest, tie-to-even. For other rounding modes, it might be off by 1,
// which is corrected below.
if (LIBC_UNLIKELY(diff > 0.5f))
return r + 1.0f;
if (LIBC_UNLIKELY(diff < -0.5f))
return r - 1.0f;
return r;
}
return x;
}
LIBC_INLINE double nearest_integer(double x) {
if (x < 0x1p53 && x > -0x1p53) {
double r = x < 0 ? (x - 0x1.0p52) + 0x1.0p52 : (x + 0x1.0p52) - 0x1.0p52;
double diff = x - r;
// The expression above is correct for the default rounding mode, round-to-
// nearest, tie-to-even. For other rounding modes, it might be off by 1,
// which is corrected below.
if (LIBC_UNLIKELY(diff > 0.5))
return r + 1.0;
if (LIBC_UNLIKELY(diff < -0.5))
return r - 1.0;
return r;
}
return x;
}
} // namespace fputil
} // namespace __llvm_libc
#endif
#endif // LLVM_LIBC_SRC_SUPPORT_FPUTIL_NEAREST_INTEGER_H
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