2505b2ca46
Because the [-1, 1) lerp can handle a higher sampling rate in t, decrease the t step to ensure everything is covered. The limit needs to be trimmed by a 1/65536 to allow the older lerps to run properly. Remove the scaled test cases. They no longer make sense. Change-Id: Ida841d65ebe794ba5d0ae67dfb145268764ec6a2 Reviewed-on: https://skia-review.googlesource.com/c/skia/+/448101 Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
109 lines
3.0 KiB
C++
109 lines
3.0 KiB
C++
/*
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* Copyright 2021 Google LLC
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#include <algorithm>
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#include <cmath>
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#include <cstdio>
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#include <cstdint>
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#include "QMath.h"
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struct Stats {
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int diff_8_bits = 0;
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int max_diff = 0;
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int min_diff = 0;
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int64_t total = 0;
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void log(int16_t golden, int16_t candidate) {
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int diff = candidate - golden;
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max_diff = std::max(max_diff, diff);
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min_diff = std::min(min_diff, diff);
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diff_8_bits += candidate != golden;
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total++;
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}
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void print() const {
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printf("8-bit diff: %d - %g%%\n", diff_8_bits, 100.0 * diff_8_bits / total);
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printf("differences min: %d max: %d\n", min_diff, max_diff);
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printf("total: %lld\n", total);
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}
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};
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static float golden_lerp(float t, int16_t a, int16_t b) {
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return (1.0f - t) * a + t * b;
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}
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template <int logPixelScale>
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static int16_t saturating_lerp(float t, int16_t a, int16_t b) {
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const int16_t half = 1 << (logPixelScale - 1);
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Q15 qt(floor(t * 32768.f + 0.5f));
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Q15 qa(a << logPixelScale);
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Q15 qb(b << logPixelScale);
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Q15 answer = simulate_neon_vqrdmulhq_s16(qt, qb - qa) + qa;
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return (answer[0] + half) >> logPixelScale;
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}
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template <int logPixelScale>
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static int16_t ssse3_lerp(float t, int16_t a, int16_t b) {
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const int16_t half = 1 << (logPixelScale - 1);
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Q15 qt(floor(t * 32768.f + 0.5f));
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Q15 qa(a << logPixelScale);
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Q15 qb(b << logPixelScale);
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Q15 answer = simulate_ssse3_mm_mulhrs_epi16(qt, qb - qa) + qa;
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return (answer[0] + half) >> logPixelScale;
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}
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// Change of parameters on t from [0, 1) to [-1, 1). This cuts the number if differences in half.
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template <int logPixelScale>
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static int16_t balanced_lerp(float t, int16_t a, int16_t b) {
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const int16_t half = 1 << logPixelScale;
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// t on [-1, 1).
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Q15 qt (floor(t * 65536.0f - 32768.0f + 0.5f));
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// need to pick logPixelScale to scale by addition 1/2.
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Q15 qw ((b - a) << logPixelScale);
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Q15 qm ((a + b) << logPixelScale);
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Q15 answer = simulate_ssse3_mm_mulhrs_epi16(qt, qw) + qm;
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// Extra shift to divide by 2.
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return (answer[0] + half) >> (logPixelScale + 1);
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}
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template <typename Lerp>
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static Stats check_lerp(Lerp lerp) {
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Stats stats;
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for (float t = 0; t < 1.0f - 1.0f / 65536.0f ; t += 1.0f/65536.0f)
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for (int a = 255; a >= 0; a--)
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for (int b = 255; b >= 0; b--) {
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float l = golden_lerp(t, a, b);
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int16_t golden = floor(l + 0.5f);
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int16_t candidate = lerp(t, a, b);
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stats.log(golden, candidate);
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}
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return stats;
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}
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int main() {
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Stats stats;
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printf("Using vqrdmulhq_s16...\n");
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stats = check_lerp(saturating_lerp<7>);
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stats.print();
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printf("\nUsing mm_mulhrs_epi16...\n");
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stats = check_lerp(ssse3_lerp<7>);
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stats.print();
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printf("\nInterval [-1, 1) mm_mulhrs_epi16...\n");
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stats = check_lerp(balanced_lerp<7>);
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stats.print();
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printf("Done.");
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return 0;
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}
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