X-Git-Url: http://nsz.repo.hu/git/?a=blobdiff_plain;f=src%2Fmath%2Flogl.c;h=03c5188fd9d79389d938cff1b6900ea90fa4aaf3;hb=a2a328bd896fa909542b492601e3689119b95de0;hp=ffd8103813eade25cc51b70944b93d78a49b8cf8;hpb=97721a5508415a2f10eb068e022093811c9ff8be;p=musl

diff --git a/src/math/logl.c b/src/math/logl.c
index ffd81038..03c5188f 100644
--- a/src/math/logl.c
+++ b/src/math/logl.c
@@ -35,9 +35,9 @@
  *
  *     log(1+x) = x - 0.5 x**2 + x**3 P(x)/Q(x).
  *
- * Otherwise, setting  z = 2(x-1)/x+1),
+ * Otherwise, setting  z = 2(x-1)/(x+1),
  *
- *     log(x) = z + z**3 P(z)/Q(z).
+ *     log(x) = log(1+z/2) - log(1-z/2) = z + z**3 P(z)/Q(z).
  *
  *
  * ACCURACY:
@@ -50,11 +50,6 @@
  * In the tests over the interval exp(+-10000), the logarithms
  * of the random arguments were uniformly distributed over
  * [-10000, +10000].
- *
- * ERROR MESSAGES:
- *
- * log singularity:  x = 0; returns -INFINITY
- * log domain:       x < 0; returns NAN
  */
 
 #include "libm.h"
@@ -121,8 +116,8 @@ long double logl(long double x)
 		return x;
 	if (x <= 0.0) {
 		if (x == 0.0)
-			return -INFINITY;
-		return NAN;
+			return -1/(x*x); /* -inf with divbyzero */
+		return 0/0.0f; /* nan with invalid */
 	}
 
 	/* separate mantissa from exponent */
@@ -132,7 +127,7 @@ long double logl(long double x)
 	x = frexpl(x, &e);
 
 	/* logarithm using log(x) = z + z**3 P(z)/Q(z),
-	 * where z = 2(x-1)/x+1)
+	 * where z = 2(x-1)/(x+1)
 	 */
 	if (e > 2 || e < -2) {
 		if (x < SQRTH) {  /* 2(2x-1)/(2x+1) */