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// Copyright 2020 Google LLC
//
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree.
#include <assert.h>
#include <stddef.h>
#include <emmintrin.h>
#include <xnnpack/math-stubs.h>
void xnn_math_f32_roundz__sse2_cvt(
size_t n,
const float* input,
float* output)
{
assert(n % (4 * sizeof(float)) == 0);
// This magic number serves two purposes:
// 1. Set the bit corresponding to the sign of a floating-point number in a bitmask.
// 2. Check if the input to CVTTPS2DQ (_mm_cvttps_epi32) is out-of-range, which results in 0x80000000 output.
const __m128i vmagic = _mm_set1_epi32(0x80000000);
for (; n != 0; n -= 4 * sizeof(float)) {
const __m128 vx = _mm_load_ps(input);
input += 4;
// Convert floating-point value x to integer, with rounding towards zero.
// If x is beyond [-2**31, 2**31-1] range or x is NaN, the result is -2**31 (0x80000000).
const __m128i vintx = _mm_cvttps_epi32(vx);
// Compute bitmask for the bits we want to copy from the rounded x. Other bits will be copied from x.
// If x is out-of-range for CVTTPS2DQ, we want all bits from x.
// If x is in-range for CVTTPS2DQ, we want all but the sign bit from the rounded x and the sign bit from x.
const __m128 vrndmask = _mm_castsi128_ps(_mm_or_si128(vmagic, _mm_cmpeq_epi32(vintx, vmagic)));
// Convert integer back to floating-point.
// We binary OR the result with the sign of x to restore the sign of negative zero.
const __m128 vrndx = _mm_cvtepi32_ps(vintx);
// Combine x rounded via conversion to integer and the initial x value.
// For -2**31 < x < 2**31, the result is x rounded via conversion to integer.
// Otherwise (including NaN inputs), the result is x itself.
const __m128 vy = _mm_or_ps(_mm_and_ps(vx, vrndmask), _mm_andnot_ps(vrndmask, vrndx));
_mm_store_ps(output, vy);
output += 4;
}
}