math: add dummy implementations of 128 bit long double functions

[musl] / src / math / logl.c

diff --git a/src/math/logl.c b/src/math/logl.c
index ffd8103..5d53659 100644 (file)
--- 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) */
@@ -171,4 +166,10 @@ long double logl(long double x)
        z = z + e * C1; /* This sum has an error of 1/2 lsb. */
        return z;
 }
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
+// TODO: broken implementation to make things compile
+long double logl(long double x)
+{
+       return log(x);
+}
 #endif