Signed requantization evaluation stubs and unit tests
PiperOrigin-RevId: 323887449
diff --git a/src/qs8-requantization/fp32-sse2.c b/src/qs8-requantization/fp32-sse2.c
new file mode 100644
index 0000000..b7518c9
--- /dev/null
+++ b/src/qs8-requantization/fp32-sse2.c
@@ -0,0 +1,94 @@
+// 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 <emmintrin.h>
+
+#include <xnnpack/requantization-stubs.h>
+
+
+void xnn_qs8_requantize_fp32__sse2(
+ size_t n,
+ const int32_t* input,
+ float scale,
+ int8_t zero_point,
+ int8_t qmin,
+ int8_t qmax,
+ int8_t* output)
+{
+ assert(n % 16 == 0);
+ assert(scale < 1.0f);
+ assert(scale >= 0x1.0p-32f);
+
+ const __m128 vscale = _mm_set1_ps(scale);
+ const __m128i vzero_point = _mm_set1_epi16((short) (uint16_t) zero_point);
+ const __m128i vqmin = _mm_set1_epi8((char) qmin);
+ const __m128i vqmax = _mm_set1_epi8((char) qmax);
+ for (; n != 0; n -= 16) {
+ const __m128i x = _mm_loadu_si128((const __m128i*) input);
+ const __m128i y = _mm_loadu_si128((const __m128i*) (input + 4));
+ const __m128i z = _mm_loadu_si128((const __m128i*) (input + 8));
+ const __m128i w = _mm_loadu_si128((const __m128i*) (input + 12));
+ input += 16;
+
+ // Convert int32_t input to FP32 and multiply by FP32 scale.
+ // Both operations involve statistically unbiased roundings (with default MXCSR rounding mode):
+ // - Large int32_t values can't be exactly represented as FP32. CVTDQ2PS instruction on x86 would round it
+ // according to nearest FP32 value with ties to even (assuming default MXCSR rounding mode).
+ // - Product of two FP32 values is generally not exactly representation as an FP32 value, and will be rounded
+ // to nearest FP32 value with ties to even with default MXCSR rounding mode.
+ const __m128 x_scaled = _mm_mul_ps(_mm_cvtepi32_ps(x), vscale);
+ const __m128 y_scaled = _mm_mul_ps(_mm_cvtepi32_ps(y), vscale);
+ const __m128 z_scaled = _mm_mul_ps(_mm_cvtepi32_ps(z), vscale);
+ const __m128 w_scaled = _mm_mul_ps(_mm_cvtepi32_ps(w), vscale);
+
+ // Convert scaled FP32 result to int32_t using CVTPS2DQ instruction from x86 SSE2. CVTPS2DQ instruction rounds
+ // result according to nearest FP32 value with ties to even (assuming default MXCSR rounding mode).
+ // However, when conversion overflows, it produces INT32_MIN as a result. For large positive inputs the result
+ // of conversion can become negative, which affects the final requantization result. Note that on x86 SSE2 we
+ // have e.g. int32_t(float(INT32_MAX)) == INT32_MIN! This happens because float(INT32_MAX) rounds to 2**31,
+ // which overflows int32_t when it is converted back to integer.
+ //
+ // Thankfully, we can prove that overflow never happens in this requantization scheme. The largest positive
+ // input is INT32_MAX (2**31 - 1), which turns into 2**31 when converted to float. The largest scale value
+ // is 0x1.FFFFFEp-1. When multiplied together, the result is 2147483520 (compare to INT32_MAX = 2147483647),
+ // which fits into int32_t without overflow.
+ const __m128i x_rounded = _mm_cvtps_epi32(x_scaled);
+ const __m128i y_rounded = _mm_cvtps_epi32(y_scaled);
+ const __m128i z_rounded = _mm_cvtps_epi32(z_scaled);
+ const __m128i w_rounded = _mm_cvtps_epi32(w_scaled);
+
+ // Standard final sequence on x86 SSE2:
+ // - Pack to int16_t and saturate
+ // - Add zero point
+ // - Clamp between qmin and qmax
+ // - Pack to int8_t and saturate
+ const __m128i xy_packed = _mm_adds_epi16(_mm_packs_epi32(x_rounded, y_rounded), vzero_point);
+ const __m128i zw_packed = _mm_adds_epi16(_mm_packs_epi32(z_rounded, w_rounded), vzero_point);
+ const __m128i xy_clamped = _mm_max_epi16(_mm_min_epi16(xy_packed, vqmax), vqmin);
+ const __m128i zw_clamped = _mm_max_epi16(_mm_min_epi16(zw_packed, vqmax), vqmin);
+ const __m128i xyzw_clamped = _mm_packs_epi16(xy_clamped, zw_clamped);
+
+ // 4x CVTDQ2PS
+ // 4x MULPS
+ // 4x CVTPS2DQ
+ // 2x PACKSSDW
+ // 2x PADDSW
+ // 2x PMAXSW
+ // 2x PMINSW
+ // 1x PACKSSWB
+ // ---------------------
+ // 21 instructions total
+
+ _mm_storeu_si128((__m128i*) output, xyzw_clamped);
+ output += 16;
+ }
+}