Clean up SkFloatBits
- remove dead code
- rewrite float -> int converters
The strategy for the new converters is:
- convert input to double
- floor/ceil/round in double space
- pin that double to [SK_MinS32, SK_MaxS32]
- truncate that double to int32_t
This simpler strategy does not work:
- floor/ceil/round in float space
- pin that float to [SK_MinS32, SK_MaxS32]
- truncate that float to int32_t
SK_MinS32 and SK_MaxS32 are not representable as floats:
they round to the nearest float, ±2^31, which makes the
pin insufficient for floats near SK_MinS32 (-2^31+1) or
SK_MaxS32 (+2^31-1).
float only has 24 bits of precision, and we need 31.
double can represent all integers up to 50-something bits.
An alternative is to pin in float to ±2147483520, the last
exactly representable float before SK_MaxS32 (127 too small).
Our tests test that we round as floor(x+0.5), which can
return different numbers than round(x) for negative x.
So this CL explicitly uses floor(x+0.5).
I've updated the tests with ±inf and ±NaN, and tried to
make them a little clearer, especially using SK_MinS32
instead of -SK_MaxS32.
I have not timed anything here. I have never seen any of these
methods in a profile.
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2012333003
Review-Url: https://codereview.chromium.org/2012333003
diff --git a/tests/MathTest.cpp b/tests/MathTest.cpp
index ec1f936..23785f7 100644
--- a/tests/MathTest.cpp
+++ b/tests/MathTest.cpp
@@ -209,34 +209,29 @@
/* returns true if a == b as resulting from (int)x. Since it is undefined
what to do if the float exceeds 2^32-1, we check for that explicitly.
*/
-static bool equal_float_native_skia(float x, uint32_t ni, uint32_t si) {
- if (!(x == x)) { // NAN
- return ((int32_t)si) == SK_MaxS32 || ((int32_t)si) == SK_MinS32;
+static bool equal_float_native_skia(float x, int32_t ni, int32_t si) {
+ // When the float is out of integer range (NaN, above, below),
+ // the C cast is undefined, but Skia's methods should have clamped.
+ if (!(x == x)) { // NaN
+ return si == SK_MaxS32 || si == SK_MinS32;
}
- // for out of range, C is undefined, but skia always should return NaN32
if (x > SK_MaxS32) {
- return ((int32_t)si) == SK_MaxS32;
+ return si == SK_MaxS32;
}
- if (x < -SK_MaxS32) {
- return ((int32_t)si) == SK_MinS32;
+ if (x < SK_MinS32) {
+ return si == SK_MinS32;
}
return si == ni;
}
static void assert_float_equal(skiatest::Reporter* reporter, const char op[],
- float x, uint32_t ni, uint32_t si) {
+ float x, int32_t ni, int32_t si) {
if (!equal_float_native_skia(x, ni, si)) {
ERRORF(reporter, "%s float %g bits %x native %x skia %x\n",
op, x, SkFloat2Bits(x), ni, si);
}
}
-static void test_float_cast(skiatest::Reporter* reporter, float x) {
- int ix = (int)x;
- int iix = SkFloatToIntCast(x);
- assert_float_equal(reporter, "cast", x, ix, iix);
-}
-
static void test_float_floor(skiatest::Reporter* reporter, float x) {
int ix = (int)floor(x);
int iix = SkFloatToIntFloor(x);
@@ -257,23 +252,17 @@
}
static void test_float_conversions(skiatest::Reporter* reporter, float x) {
- test_float_cast(reporter, x);
test_float_floor(reporter, x);
test_float_round(reporter, x);
test_float_ceil(reporter, x);
}
-static void test_int2float(skiatest::Reporter* reporter, int ival) {
- float x0 = (float)ival;
- float x1 = SkIntToFloatCast(ival);
- REPORTER_ASSERT(reporter, x0 == x1);
-}
-
static void unittest_fastfloat(skiatest::Reporter* reporter) {
SkRandom rand;
size_t i;
static const float gFloats[] = {
+ 0.f/0.f, -0.f/0.f, 1.f/0.f, -1.f/0.f,
0.f, 1.f, 0.5f, 0.499999f, 0.5000001f, 1.f/3,
0.000000001f, 1000000000.f, // doesn't overflow
0.0000000001f, 10000000000.f // does overflow
@@ -289,17 +278,6 @@
float x = nextFloat(rand);
test_float_conversions(reporter, x);
}
-
- test_int2float(reporter, 0);
- test_int2float(reporter, 1);
- test_int2float(reporter, -1);
- for (i = 0; i < 100000; i++) {
- // for now only test ints that are 24bits or less, since we don't
- // round (down) large ints the same as IEEE...
- int ival = rand.nextU() & 0xFFFFFF;
- test_int2float(reporter, ival);
- test_int2float(reporter, -ival);
- }
}
}