jumper, implement 2.2 stages with approx_powf

My main interest is getting rid of weird code, but it's also faster.
The new bench drops from 667 to 412.

Change-Id: Ibf889601284cf925780320c828394f79937dc705
Reviewed-on: https://skia-review.googlesource.com/14035
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/tests/ParametricStageTest.cpp b/tests/ParametricStageTest.cpp
index 5810148454..0185abcb36 100644
--- a/tests/ParametricStageTest.cpp
+++ b/tests/ParametricStageTest.cpp
@@ -73,3 +73,36 @@ DEF_TEST(Parametric_inv_1dot8, r) { check_error(r, 1/510.0f, 1/1.8f); }
 DEF_TEST(Parametric_inv_2dot0, r) { check_error(r, 1/510.0f, 1/2.0f); }
 DEF_TEST(Parametric_inv_2dot2, r) { check_error(r, 1/510.0f, 1/2.2f); }
 DEF_TEST(Parametric_inv_2dot4, r) { check_error(r, 1/510.0f, 1/2.4f); }
+
+// As above, checking that the stage implements gamma within limit.
+static void check_error(skiatest::Reporter* r, float limit,
+                        float gamma, SkRasterPipeline::StockStage stage) {
+
+    // We expect the gamma will only be applied to R,G,B, leaving A alone.
+    // So this isn't quite exhaustive, but it's pretty good.
+    float in[256], out[256];
+    for (int i = 0; i < 256; i++) {
+        in [i] = i / 255.0f;
+        out[i] = 0.0f;  // Not likely important.  Just being tidy.
+    }
+
+    const float* ip = in;
+    float*       op = out;
+
+    SkRasterPipeline p;
+    p.append(SkRasterPipeline::load_f32, &ip);
+    p.append(stage);
+    p.append(SkRasterPipeline::store_f32, &op);
+    p.run(0, 256/4);
+
+    for (int i = 0; i < 256; i++) {
+        float want = powf(i/255.0f, (i%4) == 3 ? 1.0f
+                                               : gamma);
+        float err = fabsf(out[i] - want);
+        if (err > limit) {
+            ERRORF(r, "At %d, error was %g (got %g, want %g)", i, err, out[i], want);
+        }
+    }
+}
+DEF_TEST(from_2dot2, r) { check_error(r, 1/510.f, 2.2f,  SkRasterPipeline::from_2dot2); }
+DEF_TEST(  to_2dot2, r) { check_error(r, 1/510.f, 1/2.2f,SkRasterPipeline::  to_2dot2); }