constexpr NaN,+Inf,-Inf

Reading extern values meant these couldn't be compile-time constants.

math.h has INFINITY, which is macro that is supposed to expand to float +inf.
On MSVC it seems it's natively a double, so we cast just to make sure.

There's nan(const char*) in math.h for NaN too, but I don't trust that
to be compile-time evaluated.  So instead, we keep reinterpreting a bit pattern.

I did try to write

    static constexpr float float_nan() { ... }

and completely failed.  constexpr seems a bit too restrictive in C++11 to make
it work, but Clang kept telling me, you'll be able to do this with C++14.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2233853002

Review-Url: https://codereview.chromium.org/2233853002

1 files changed, 4 insertions, 7 deletions

diff --git a/include/private/SkFloatingPoint.h b/include/private/SkFloatingPoint.h
index a7aa50cf9f..8d8843eb58 100644
--- a/include/private/SkFloatingPoint.h
+++ b/include/private/SkFloatingPoint.h
@@ -100,13 +100,10 @@ static inline float sk_float_pow(float base, float exp) {
 #define sk_double_round2int(x)      (int)floor((x) + 0.5f)
 #define sk_double_ceil2int(x)       (int)ceil(x)
 
-extern const uint32_t gIEEENotANumber;
-extern const uint32_t gIEEEInfinity;
-extern const uint32_t gIEEENegativeInfinity;
-
-#define SK_FloatNaN                 (*SkTCast<const float*>(&gIEEENotANumber))
-#define SK_FloatInfinity            (*SkTCast<const float*>(&gIEEEInfinity))
-#define SK_FloatNegativeInfinity    (*SkTCast<const float*>(&gIEEENegativeInfinity))
+static const uint32_t kIEEENotANumber = 0x7fffffff;
+#define SK_FloatNaN                 (*SkTCast<const float*>(&kIEEENotANumber))
+#define SK_FloatInfinity            (+(float)INFINITY)
+#define SK_FloatNegativeInfinity    (-(float)INFINITY)
 
 static inline float sk_float_rsqrt_portable(float x) {
     // Get initial estimate.