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authorSzabolcs Nagy <nsz@port70.net>2013-09-05 12:26:26 +0000
committerSzabolcs Nagy <nsz@port70.net>2013-09-05 12:26:26 +0000
commit101e6012856918440b5d7474739c3fc22a8d3b85 (patch)
tree04b79d042e6dd3dda62afeecc9e9c80627616867 /src/math/acoshf.c
parent02343946215a7ae03634c6490abcc69da68df589 (diff)
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math: fix acoshf on negative values
acosh(x) is invalid for x<1, acoshf tried to be clever using
signed comparisions to handle all x<2 the same way, but the
formula was wrong on large negative values.
Diffstat (limited to 'src/math/acoshf.c')
-rw-r--r--src/math/acoshf.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/src/math/acoshf.c b/src/math/acoshf.c
index 4596085e..16550f19 100644
--- a/src/math/acoshf.c
+++ b/src/math/acoshf.c
@@ -3,14 +3,15 @@
 /* acosh(x) = log(x + sqrt(x*x-1)) */
 float acoshf(float x)
 {
-	union {float f; int32_t i;} u = {.f = x};
+	union {float f; uint32_t i;} u = {x};
+	uint32_t a = u.i & 0x7fffffff;
 
-	if (u.i < 0x3f800000+(1<<23))
-		/* x < 2, invalid if x < 1 or nan */
+	if (a < 0x3f800000+(1<<23))
+		/* |x| < 2, invalid if x < 1 or nan */
 		/* up to 2ulp error in [1,1.125] */
 		return log1pf(x-1 + sqrtf((x-1)*(x-1)+2*(x-1)));
-	if (u.i < 0x3f800000+(12<<23))
-		/* x < 0x1p12 */
+	if (a < 0x3f800000+(12<<23))
+		/* |x| < 0x1p12 */
 		return logf(2*x - 1/(x+sqrtf(x*x-1)));
 	/* x >= 0x1p12 */
 	return logf(x) + 0.693147180559945309417232121458176568f;