Make SkPMFloats store floats in [0,255] instead of [0,1].

This pushes the cost of the *255 and *1/255 conversions onto only those code
paths that need it.  We're not doing it any more efficiently than can be done
with Sk4f.

In microbenchmark isolation, this is about a 15% speedup.

BUG=skia:
NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/973603002

1 files changed, 6 insertions, 10 deletions

diff --git a/src/opts/SkPMFloat_neon.h b/src/opts/SkPMFloat_neon.h
index 004b6588dd..15ba3a58e4 100644
--- a/src/opts/SkPMFloat_neon.h
+++ b/src/opts/SkPMFloat_neon.h
@@ -2,11 +2,10 @@
 #include <arm_neon.h>
 
 // For set(), we widen our 8 bit components (fix8) to 8-bit components in 16 bits (fix8_16),
-// then widen those to 8-bit-in-32-bits (fix8_32), convert those to floats (scaled),
-// then finally scale those down from [0.0f, 255.0f] to [0.0f, 1.0f] into fColor.
+// then widen those to 8-bit-in-32-bits (fix8_32), and finally convert those to floats.
 
-// get() and clamped() do the opposite, working from [0.0f, 1.0f] floats to [0.0f, 255.0f],
-// to 8-bit-in-32-bit, to 8-bit-in-16-bit, back down to 8-bit components.
+// get() and clamped() do the opposite, working from floats to 8-bit-in-32-bit,
+// to 8-bit-in-16-bit, back down to 8-bit components.
 // clamped() uses vqmovn to clamp while narrowing instead of just narrowing with vmovn.
 
 inline void SkPMFloat::set(SkPMColor c) {
@@ -14,15 +13,13 @@ inline void SkPMFloat::set(SkPMColor c) {
     uint8x8_t   fix8    = (uint8x8_t)vdup_n_u32(c);
     uint16x8_t  fix8_16 = vmovl_u8(fix8);
     uint32x4_t  fix8_32 = vmovl_u16(vget_low_u16(fix8_16));
-    float32x4_t scaled  = vcvtq_f32_u32(fix8_32);
-    vst1q_f32(fColor, vmulq_f32(scaled, vdupq_n_f32(1.0f/255.0f)));
+    vst1q_f32(fColor, vcvtq_f32_u32(fix8_32));
     SkASSERT(this->isValid());
 }
 
 inline SkPMColor SkPMFloat::get() const {
     SkASSERT(this->isValid());
-    float32x4_t scaled  = vmulq_f32(vld1q_f32(fColor), vdupq_n_f32(255.0f));
-    uint32x4_t  fix8_32 = vcvtq_u32_f32(scaled);
+    uint32x4_t  fix8_32 = vcvtq_u32_f32(vld1q_f32(fColor));
     uint16x4_t  fix8_16 = vmovn_u32(fix8_32);
     uint8x8_t   fix8    = vmovn_u16(vcombine_u16(fix8_16, vdup_n_u16(0)));
     SkPMColor c = vget_lane_u32((uint32x2_t)fix8, 0);
@@ -31,8 +28,7 @@ inline SkPMColor SkPMFloat::get() const {
 }
 
 inline SkPMColor SkPMFloat::clamped() const {
-    float32x4_t scaled  = vmulq_f32(vld1q_f32(fColor), vdupq_n_f32(255.0f));
-    uint32x4_t  fix8_32 = vcvtq_u32_f32(scaled);
+    uint32x4_t  fix8_32 = vcvtq_u32_f32(vld1q_f32(fColor));
     uint16x4_t  fix8_16 = vqmovn_u32(fix8_32);
     uint8x8_t   fix8    = vqmovn_u16(vcombine_u16(fix8_16, vdup_n_u16(0)));
     SkPMColor c = vget_lane_u32((uint32x2_t)fix8, 0);