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// Copyright (c) Facebook, Inc. and its affiliates.
// All rights reserved.
//
// Copyright 2019 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 <stdint.h>
#include <stddef.h>
#include <fp16/bitcasts.h>
#include <xnnpack/math.h>
#include <xnnpack/requantization-stubs.h>
void xnn_qs8_requantize_rndna__scalar_signed64(
size_t n,
const int32_t* input,
float scale,
int8_t zero_point,
int8_t qmin,
int8_t qmax,
int8_t* output)
{
assert(n % 4 == 0);
assert(scale < 1.0f);
assert(scale >= 0x1.0p-32f);
const uint32_t scale_bits = fp32_to_bits(scale);
const int32_t multiplier = ((int32_t) scale_bits & INT32_C(0x007FFFFF)) | INT32_C(0x00800000);
const uint32_t shift = 127 + 23 - (scale_bits >> 23);
assert(shift >= 24);
assert(shift < 56);
const int64_t rounding = INT64_C(1) << (shift - 1);
const int32_t smin = (int32_t) qmin - (int32_t) zero_point;
const int32_t smax = (int32_t) qmax - (int32_t) zero_point;
for (; n != 0; n -= 4) {
const int32_t x = input[0];
const int32_t y = input[1];
const int32_t z = input[2];
const int32_t w = input[3];
input += 4;
// Compute full 64-bit product of signed 32-bit factors.
//
// Note: multiplier can be treated as either signed or unsigned.
const int64_t x_product = (int64_t) x * (int64_t) multiplier;
const int64_t y_product = (int64_t) y * (int64_t) multiplier;
const int64_t z_product = (int64_t) z * (int64_t) multiplier;
const int64_t w_product = (int64_t) w * (int64_t) multiplier;
// Adjust product before subsequent shift with rounding up to simulate shift with rounding away from zero.
const int64_t x_adjusted_product = x_product - (int64_t)(x < 0);
const int64_t y_adjusted_product = y_product - (int64_t)(y < 0);
const int64_t z_adjusted_product = z_product - (int64_t)(z < 0);
const int64_t w_adjusted_product = w_product - (int64_t)(w < 0);
// Arithmetically shift the full 64-bit product right with rounding.
// Rounding is performed towards closest integer, with midpoints rounded up.
//
// Note that although rounding is precomputed, it is dependent on shift value, and on processors with 64-bit
// "right shift with rounding" instruction each line below can be represented by just one such instruction
// (e.g. VRSHL.S64 on ARM NEON, SRSHL in ARM64 Advanced SIMD).
const int32_t x_scaled = (int32_t) asr_s64(x_adjusted_product + rounding, shift);
const int32_t y_scaled = (int32_t) asr_s64(y_adjusted_product + rounding, shift);
const int32_t z_scaled = (int32_t) asr_s64(z_adjusted_product + rounding, shift);
const int32_t w_scaled = (int32_t) asr_s64(w_adjusted_product + rounding, shift);
// Clamp scaled value with zero point between (qmin - zero point) and (qmax - zero point).
const int32_t x_clamped = math_min_s32(math_max_s32(x_scaled, smin), smax);
const int32_t y_clamped = math_min_s32(math_max_s32(y_scaled, smin), smax);
const int32_t z_clamped = math_min_s32(math_max_s32(z_scaled, smin), smax);
const int32_t w_clamped = math_min_s32(math_max_s32(w_scaled, smin), smax);
// Add zero point to clamped value.
// The result is guaranteed to be in [qmin, qmax] range.
//
// This addition can not be safely done before clamping, because scaled values are in [-2147483520, 2147483519]
// range, so addition of zero point (which can be up to 127) can overflow signed 32-bit integer.
const int32_t x_biased = x_clamped + zero_point;
const int32_t y_biased = y_clamped + zero_point;
const int32_t z_biased = z_clamped + zero_point;
const int32_t w_biased = w_clamped + zero_point;
output[0] = (int8_t) x_biased;
output[1] = (int8_t) y_biased;
output[2] = (int8_t) z_biased;
output[3] = (int8_t) w_biased;
output += 4;
}
}