de-proc sk_float_rsqrt

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

BUG=skia:
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Committed: https://skia.googlesource.com/skia/+/efcc125acd2d71eb077caf6db65fdd6b9eb1dc0d

Review URL: https://codereview.chromium.org/1616013003

6 files changed, 22 insertions, 55 deletions

diff --git a/include/private/SkFloatingPoint.h b/include/private/SkFloatingPoint.h
index f7ee816b12..ffed5c0747 100644
--- a/include/private/SkFloatingPoint.h
+++ b/include/private/SkFloatingPoint.h
@@ -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
 }
 
diff --git a/src/core/SkOpts.cpp b/src/core/SkOpts.cpp
index 28dd1afc71..669401b417 100644
--- a/src/core/SkOpts.cpp
+++ b/src/core/SkOpts.cpp
@@ -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;
diff --git a/src/core/SkOpts.h b/src/core/SkOpts.h
index 1a9820b417..41ad8ebfe8 100644
--- a/src/core/SkOpts.h
+++ b/src/core/SkOpts.h
@@ -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);
diff --git a/src/opts/SkFloatingPoint_opts.h b/src/opts/SkFloatingPoint_opts.h
deleted file mode 100644
index 8b6536ad7f..0000000000
--- a/src/opts/SkFloatingPoint_opts.h
+++ /dev/null
@@ -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
diff --git a/src/opts/SkOpts_neon.cpp b/src/opts/SkOpts_neon.cpp
index 9cff2298e4..dcb057e1fe 100644
--- a/src/opts/SkOpts_neon.cpp
+++ b/src/opts/SkOpts_neon.cpp
@@ -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;
diff --git a/tests/MathTest.cpp b/tests/MathTest.cpp
index 24e46f3097..de7ad1db78 100644
--- a/tests/MathTest.cpp
+++ b/tests/MathTest.cpp
@@ -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();