commit a9c199c99b4ac6b662c520ae16ec84eec2a00ee3
author John Stiles <johnstiles@google.com> Fri Mar 17 12:07:22 2023 -0400
committer SkCQ <skcq-be@skia-corp.google.com.iam.gserviceaccount.com> Fri Mar 17 18:50:27 2023 +0000
tree 5d6bbb524872fa68414355a5cc54bf271b987009
parent 3213affd36d0237bb7ad20af431ab4ad2b4e3099

Implement asin and acos primitives in Raster Pipeline.

These follow the SkVM implementation very closely.

Change-Id: I0fb39f8c443e01de2140f8321c00375326be57bc
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/658019
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>

src/core/SkVM.cpp

diff --git a/src/core/SkVM.cpp b/src/core/SkVM.cpp
index 9c33e29..b063f55 100644
--- a/src/core/SkVM.cpp
+++ b/src/core/SkVM.cpp
@@ -909,16 +909,16 @@
         return x;
     }
 
-     // http://mathforum.org/library/drmath/view/54137.html
-     // referencing Handbook of Mathematical Functions,
-     //             by Milton Abramowitz and Irene Stegun
-     F32 Builder::approx_asin(F32 x) {
+    // http://mathforum.org/library/drmath/view/54137.html
+    // referencing Handbook of Mathematical Functions,
+    //             by Milton Abramowitz and Irene Stegun
+    F32 Builder::approx_asin(F32 x) {
          I32 neg = (x < 0.0f);
          x = select(neg, -x, x);
          x = SK_ScalarPI/2 - sqrt(1-x) * poly(x, -0.0187293f, 0.0742610f, -0.2121144f, 1.5707288f);
          x = select(neg, -x, x);
          return x;
-     }
+    }
 
     /*  Use 4th order polynomial approximation from https://arachnoid.com/polysolve/
      *      with 129 values of x,atan(x) for x:[0...1]

src/opts/SkRasterPipeline_opts.h

diff --git a/src/opts/SkRasterPipeline_opts.h b/src/opts/SkRasterPipeline_opts.h
index 33999c3..31cca2c 100644
--- a/src/opts/SkRasterPipeline_opts.h
+++ b/src/opts/SkRasterPipeline_opts.h
@@ -1561,6 +1561,23 @@
     return x;
 }
 
+
+// Handbook of Mathematical Functions, by Milton Abramowitz and Irene Stegun:
+// https://books.google.com/books/content?id=ZboM5tOFWtsC&pg=PA81&img=1&zoom=3&hl=en&bul=1&sig=ACfU3U2M75tG_iGVOS92eQspr14LTq02Nw&ci=0%2C15%2C999%2C1279&edge=0
+// http://screen/8YGJxUGFQ49bVX6
+SI F asin_(F x) {
+    I32 neg = (x < 0.0f);
+    x = if_then_else(neg, -x, x);
+    F poly = x * (x * (x * -0.0187293f + 0.0742610f) - 0.2121144f) + 1.5707288f;
+    x = SK_ScalarPI/2 - sqrt_(1 - x) * poly;
+    x = if_then_else(neg, -x, x);
+    return x;
+}
+
+SI F acos_(F x) {
+    return SK_ScalarPI/2 - asin_(x);
+}
+
 /*  Use identity atan(x) = pi/2 - atan(1/x) for x > 1
     By swapping y,x to ensure the ratio is <= 1, we can safely call atan_unit()
     which avoids a 2nd divide instruction if we had instead called atan().

tests/SkRasterPipelineOptsTest.cpp

diff --git a/tests/SkRasterPipelineOptsTest.cpp b/tests/SkRasterPipelineOptsTest.cpp
index 4bcc260..d4e4cea 100644
--- a/tests/SkRasterPipelineOptsTest.cpp
+++ b/tests/SkRasterPipelineOptsTest.cpp
@@ -122,6 +122,32 @@
     }
 }
 
+DEF_TEST(SkRasterPipelineOpts_Asin, r) {
+    using F = SK_OPTS_NS::F;
+
+    constexpr float kTolerance = 0.00175f;
+    for (float x = -1; x <= 1; x += 1.0f/64) {
+        F result = SK_OPTS_NS::asin_(x);
+        F expected = asinf(x);
+        F delta = SK_OPTS_NS::abs_(expected - result);
+
+        REPORTER_ASSERT(r, SK_OPTS_NS::all(delta < kTolerance));
+    }
+}
+
+DEF_TEST(SkRasterPipelineOpts_Acos, r) {
+    using F = SK_OPTS_NS::F;
+
+    constexpr float kTolerance = 0.00175f;
+    for (float x = -1; x <= 1; x += 1.0f/64) {
+        F result = SK_OPTS_NS::acos_(x);
+        F expected = acosf(x);
+        F delta = SK_OPTS_NS::abs_(expected - result);
+
+        REPORTER_ASSERT(r, SK_OPTS_NS::all(delta < kTolerance));
+    }
+}
+
 DEF_TEST(SkRasterPipelineOpts_Atan, r) {
     using F = SK_OPTS_NS::F;