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de-proc sk_float_rsqrt

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This is the first of many little baby steps to have us stop runtime-detecting NEON.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1616013003
CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Review URL: https://codereview.chromium.org/1616013003
This commit is contained in:
mtklein 2016-01-22 08:49:26 -08:00 committed by Commit bot
parent aed5717afd
commit efcc125acd
6 changed files with 22 additions and 55 deletions
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23
include/private/SkFloatingPoint.h
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@ -127,20 +127,28 @@ extern const uint32_t gIEEENegativeInfinity;
#define SK_FloatInfinity (*SkTCast<const float*>(&gIEEEInfinity))
#define SK_FloatNegativeInfinity (*SkTCast<const float*>(&gIEEENegativeInfinity))
// We forward declare this to break an #include cycle.
// (SkScalar -> SkFloatingPoint -> SkOpts.h -> SkXfermode -> SkColor -> SkScalar)
namespace SkOpts { extern float (*rsqrt)(float); }
static inline float sk_float_rsqrt_portable(float x) {
// Get initial estimate.
int i = *SkTCast<int*>(&x);
i = 0x5F1FFFF9 - (i>>1);
float estimate = *SkTCast<float*>(&i);
// One step of Newton's method to refine.
const float estimate_sq = estimate*estimate;
estimate *= 0.703952253f*(2.38924456f-x*estimate_sq);
return estimate;
}
// Fast, approximate inverse square root.
// Compare to name-brand "1.0f / sk_float_sqrt(x)". Should be around 10x faster on SSE, 2x on NEON.
static inline float sk_float_rsqrt(const float x) {
static inline float sk_float_rsqrt(float x) {
// We want all this inlined, so we'll inline SIMD and just take the hit when we don't know we've got
// it at compile time. This is going to be too fast to productively hide behind a function pointer.
//
// We do one step of Newton's method to refine the estimates in the NEON and null paths. No
// We do one step of Newton's method to refine the estimates in the NEON and portable paths. No
// refinement is faster, but very innacurate. Two steps is more accurate, but slower than 1/sqrt.
//
// Optimized constants in the null path courtesy of http://rrrola.wz.cz/inv_sqrt.html
// Optimized constants in the portable path courtesy of http://rrrola.wz.cz/inv_sqrt.html
#if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE1
return _mm_cvtss_f32(_mm_rsqrt_ss(_mm_set_ss(x)));
#elif defined(SK_ARM_HAS_NEON)
@ -153,8 +161,7 @@ static inline float sk_float_rsqrt(const float x) {
estimate = vmul_f32(estimate, vrsqrts_f32(xx, estimate_sq));
return vget_lane_f32(estimate, 0); // 1 will work fine too; the answer's in both places.
#else
// Perhaps runtime-detected NEON, or a portable fallback.
return SkOpts::rsqrt(x);
return sk_float_rsqrt_portable(x);
#endif
}

2
src/core/SkOpts.cpp
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@ -13,7 +13,6 @@
#include "SkBlitRow_opts.h"
#include "SkBlurImageFilter_opts.h"
#include "SkColorCubeFilter_opts.h"
#include "SkFloatingPoint_opts.h"
#include "SkMatrix_opts.h"
#include "SkMorphologyImageFilter_opts.h"
#include "SkSwizzler_opts.h"
@ -55,7 +54,6 @@ namespace SkOpts {
// If our global compile options are set high enough, these defaults might even be
// CPU-specialized, e.g. a typical x86-64 machine might start with SSE2 defaults.
// They'll still get a chance to be replaced with even better ones, e.g. using SSE4.1.
decltype(rsqrt) rsqrt = sk_default::rsqrt;
decltype(memset16) memset16 = sk_default::memset16;
decltype(memset32) memset32 = sk_default::memset32;
decltype(create_xfermode) create_xfermode = sk_default::create_xfermode;

3
src/core/SkOpts.h
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@ -23,9 +23,6 @@ namespace SkOpts {
// Declare function pointers here...
// Returns a fast approximation of 1.0f/sqrtf(x).
extern float (*rsqrt)(float);
// See SkUtils.h
extern void (*memset16)(uint16_t[], uint16_t, int);
extern void (*memset32)(uint32_t[], uint32_t, int);

35
src/opts/SkFloatingPoint_opts.h
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@ -1,35 +0,0 @@
/*
* Copyright 2015 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkFloatingPoint_opts_DEFINED
#define SkFloatingPoint_opts_DEFINED
#include "SkFloatingPoint.h"
namespace SK_OPTS_NS {
#if defined(SK_ARM_HAS_NEON)
static float rsqrt(float x) {
return sk_float_rsqrt(x); // This sk_float_rsqrt copy will take the NEON compile-time path.
}
#else
static float rsqrt(float x) {
// Get initial estimate.
int i = *SkTCast<int*>(&x);
i = 0x5F1FFFF9 - (i>>1);
float estimate = *SkTCast<float*>(&i);
// One step of Newton's method to refine.
const float estimate_sq = estimate*estimate;
estimate *= 0.703952253f*(2.38924456f-x*estimate_sq);
return estimate;
}
#endif
} // namespace SK_OPTS_NS
#endif//SkFloatingPoint_opts_DEFINED

2
src/opts/SkOpts_neon.cpp
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@ -12,7 +12,6 @@
#include "SkBlitRow_opts.h"
#include "SkBlurImageFilter_opts.h"
#include "SkColorCubeFilter_opts.h"
#include "SkFloatingPoint_opts.h"
#include "SkMatrix_opts.h"
#include "SkMorphologyImageFilter_opts.h"
#include "SkSwizzler_opts.h"
@ -22,7 +21,6 @@
namespace SkOpts {
void Init_neon() {
rsqrt = sk_neon::rsqrt;
memset16 = sk_neon::memset16;
memset32 = sk_neon::memset32;
create_xfermode = sk_neon::create_xfermode;

12
tests/MathTest.cpp
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@ -382,14 +382,15 @@ static void unittest_half(skiatest::Reporter* reporter) {
}
static void test_rsqrt(skiatest::Reporter* reporter) {
template <typename RSqrtFn>
static void test_rsqrt(skiatest::Reporter* reporter, RSqrtFn rsqrt) {
const float maxRelativeError = 6.50196699e-4f;
// test close to 0 up to 1
float input = 0.000001f;
for (int i = 0; i < 1000; ++i) {
float exact = 1.0f/sk_float_sqrt(input);
float estimate = sk_float_rsqrt(input);
float estimate = rsqrt(input);
float relativeError = sk_float_abs(exact - estimate)/exact;
REPORTER_ASSERT(reporter, relativeError <= maxRelativeError);
input += 0.001f;
@ -399,7 +400,7 @@ static void test_rsqrt(skiatest::Reporter* reporter) {
input = 1.0f;
for (int i = 0; i < 1000; ++i) {
float exact = 1.0f/sk_float_sqrt(input);
float estimate = sk_float_rsqrt(input);
float estimate = rsqrt(input);
float relativeError = sk_float_abs(exact - estimate)/exact;
REPORTER_ASSERT(reporter, relativeError <= maxRelativeError);
input += 0.01f;
@ -409,7 +410,7 @@ static void test_rsqrt(skiatest::Reporter* reporter) {
input = 1000000.0f;
for (int i = 0; i < 100; ++i) {
float exact = 1.0f/sk_float_sqrt(input);
float estimate = sk_float_rsqrt(input);
float estimate = rsqrt(input);
float relativeError = sk_float_abs(exact - estimate)/exact;
REPORTER_ASSERT(reporter, relativeError <= maxRelativeError);
input += 754326.f;
@ -555,7 +556,8 @@ DEF_TEST(Math, reporter) {
unittest_fastfloat(reporter);
unittest_isfinite(reporter);
unittest_half(reporter);
test_rsqrt(reporter);
test_rsqrt(reporter, sk_float_rsqrt);
test_rsqrt(reporter, sk_float_rsqrt_portable);
for (i = 0; i < 10000; i++) {
SkFixed numer = rand.nextS();