*SkTCast<int*>(float*) -> memcpy

In some build configurations (I think, GN, GCC 6, Debug) I get a warning that i is used unintialized.  This likely has something to do with GCC correctly seeing that the SkTCast construction there is illegal aliasing, and perhaps thus "doesn't happen".  Might be that if the SkTCast gets inlined, it decides its implementation is secretly kosher, and so Release builds don't see this.  None of this happens with the GCCs we have on the bots... too old?

Instead use memcpy() here, which is well defined to do what we intended.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2758

Change-Id: Iaf5c75fbd852193b0b861bf5e71450502511d102
Reviewed-on: https://skia-review.googlesource.com/2758
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>

2 files changed, 5 insertions, 13 deletions

diff --git a/bench/MathBench.cpp b/bench/MathBench.cpp
index 05a5f8a2d5..541a1052dc 100644
--- a/bench/MathBench.cpp
+++ b/bench/MathBench.cpp
@@ -126,23 +126,13 @@ private:
     typedef MathBench INHERITED;
 };
 
-static inline float SkFastInvSqrt(float x) {
-    float xhalf = 0.5f*x;
-    uint32_t i = *SkTCast<uint32_t*>(&x);
-    i = 0x5f3759df - (i>>1);
-    x = *SkTCast<float*>(&i);
-    x = x*(1.5f-xhalf*x*x);
-//    x = x*(1.5f-xhalf*x*x); // this line takes err from 10^-3 to 10^-6
-    return x;
-}
-
 class FastISqrtMathBench : public MathBench {
 public:
     FastISqrtMathBench() : INHERITED("fastIsqrt") {}
 protected:
     void performTest(float* SK_RESTRICT dst, const float* SK_RESTRICT src, int count) override {
         for (int i = 0; i < count; ++i) {
-            dst[i] = SkFastInvSqrt(src[i]);
+            dst[i] = sk_float_rsqrt(src[i]);
         }
     }
 private:
diff --git a/include/private/SkFloatingPoint.h b/include/private/SkFloatingPoint.h
index 8d8843eb58..6a6edf3651 100644
--- a/include/private/SkFloatingPoint.h
+++ b/include/private/SkFloatingPoint.h
@@ -107,9 +107,11 @@ static const uint32_t kIEEENotANumber = 0x7fffffff;
 
 static inline float sk_float_rsqrt_portable(float x) {
     // Get initial estimate.
-    int i = *SkTCast<int*>(&x);
+    int i;
+    memcpy(&i, &x, 4);
     i = 0x5F1FFFF9 - (i>>1);
-    float estimate = *SkTCast<float*>(&i);
+    float estimate;
+    memcpy(&estimate, &i, 4);
 
     // One step of Newton's method to refine.
     const float estimate_sq = estimate*estimate;