float components in xfermodes

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1623483002

TBR=mtklein

Review URL: https://codereview.chromium.org/1634273002
diff --git a/src/core/SkPM4fPriv.h b/src/core/SkPM4fPriv.h
index a4cec5c..81aff70 100644
--- a/src/core/SkPM4fPriv.h
+++ b/src/core/SkPM4fPriv.h
@@ -27,12 +27,12 @@
     return SkNx_cast<float>(Sk4b::Load((const uint8_t*)&b4));
 }
 
-static inline Sk4f s2l(const Sk4f& s4) {
+static inline Sk4f srgb_to_linear(const Sk4f& s4) {
     return set_alpha(s4 * s4, get_alpha(s4));
 }
 
-static inline Sk4f l2s(const Sk4f& l4) {
-    return set_alpha(l4.rsqrt1() * l4, get_alpha(l4));
+static inline Sk4f linear_to_srgb(const Sk4f& l4) {
+    return set_alpha(l4.sqrt(), get_alpha(l4));
 }
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
@@ -42,7 +42,7 @@
 }
 
 static inline Sk4f Sk4f_fromS32(uint32_t src) {
-    return s2l(to_4f(src) * Sk4f(1.0f/255));
+    return srgb_to_linear(to_4f(src) * Sk4f(1.0f/255));
 }
 
 static inline uint32_t Sk4f_toL32(const Sk4f& x4) {
@@ -50,72 +50,5 @@
 }
 
 static inline uint32_t Sk4f_toS32(const Sk4f& x4) {
-    return to_4b(l2s(x4) * Sk4f(255) + Sk4f(0.5f));
+    return to_4b(linear_to_srgb(x4) * Sk4f(255) + Sk4f(0.5f));
 }
-
-///////////////////////////////////////////////////////////////////////////////////////////////////
-
-static Sk4f unit_to_l255_round(const SkPM4f& pm4) {
-    return Sk4f::Load(pm4.fVec) * Sk4f(255) + Sk4f(0.5f);
-}
-
-static Sk4f unit_to_s255_round(const SkPM4f& pm4) {
-    return l2s(Sk4f::Load(pm4.fVec)) * Sk4f(255) + Sk4f(0.5f);
-}
-
-static inline void SkPM4f_l32_src_mode(SkPMColor dst[], const SkPM4f src[], int count) {
-    for (int i = 0; i < (count >> 2); ++i) {
-        SkASSERT(src[0].isUnit());
-        SkASSERT(src[1].isUnit());
-        SkASSERT(src[2].isUnit());
-        SkASSERT(src[3].isUnit());
-        Sk4f_ToBytes((uint8_t*)dst,
-                     unit_to_l255_round(src[0]), unit_to_l255_round(src[1]),
-                     unit_to_l255_round(src[2]), unit_to_l255_round(src[3]));
-        src += 4;
-        dst += 4;
-    }
-    count &= 3;
-    for (int i = 0; i < count; ++i) {
-        SkASSERT(src[i].isUnit());
-        SkNx_cast<uint8_t>(unit_to_l255_round(src[i])).store((uint8_t*)&dst[i]);
-    }
-}
-
-static inline void SkPM4f_l32_srcover_mode(SkPMColor dst[], const SkPM4f src[], int count) {
-    for (int i = 0; i < count; ++i) {
-        SkASSERT(src[i].isUnit());
-        Sk4f s4 = Sk4f::Load(src[i].fVec);
-        Sk4f d4 = Sk4f_fromL32(dst[i]);
-        dst[i] = Sk4f_toL32(s4 + d4 * Sk4f(1 - get_alpha(s4)));
-    }
-}
-
-static inline void SkPM4f_s32_src_mode(SkPMColor dst[], const SkPM4f src[], int count) {
-    for (int i = 0; i < (count >> 2); ++i) {
-        SkASSERT(src[0].isUnit());
-        SkASSERT(src[1].isUnit());
-        SkASSERT(src[2].isUnit());
-        SkASSERT(src[3].isUnit());
-        Sk4f_ToBytes((uint8_t*)dst,
-                     unit_to_s255_round(src[0]), unit_to_s255_round(src[1]),
-                     unit_to_s255_round(src[2]), unit_to_s255_round(src[3]));
-        src += 4;
-        dst += 4;
-    }
-    count &= 3;
-    for (int i = 0; i < count; ++i) {
-        SkASSERT(src[i].isUnit());
-        SkNx_cast<uint8_t>(unit_to_s255_round(src[i])).store((uint8_t*)&dst[i]);
-    }
-}
-
-static inline void SkPM4f_s32_srcover_mode(SkPMColor dst[], const SkPM4f src[], int count) {
-    for (int i = 0; i < count; ++i) {
-        SkASSERT(src[i].isUnit());
-        Sk4f s4 = Sk4f::Load(src[i].fVec);
-        Sk4f d4 = Sk4f_fromS32(dst[i]);
-        dst[i] = Sk4f_toS32(s4 + d4 * Sk4f(1 - get_alpha(s4)));
-    }
-}
-