math: expf.c cleanup

[musl] / src / math / exp.c

diff --git a/src/math/exp.c b/src/math/exp.c
index 5c0edee..5ec8f8a 100644 (file)
--- a/src/math/exp.c
+++ b/src/math/exp.c
@@ -80,7 +80,7 @@ P5   =  4.13813679705723846039e-08; /* 0x3E663769, 0x72BEA4D0 */
 
 double exp(double x)
 {
-       double hi, lo, c, z;
+       double hi, lo, c, xx;
        int k, sign;
        uint32_t hx;
 
@@ -92,24 +92,26 @@ double exp(double x)
        if (hx >= 0x40862e42) {  /* if |x| >= 709.78... */
                if (isnan(x))
                        return x;
+               if (hx == 0x7ff00000 && sign) /* -inf */
+                       return 0;
                if (x > 709.782712893383973096) {
                        /* overflow if x!=inf */
                        STRICT_ASSIGN(double, x, 0x1p1023 * x);
                        return x;
                }
                if (x < -745.13321910194110842) {
-                       /* underflow if x!=-inf */
-                       STRICT_ASSIGN(double, x, 0x1p-1000 / -x * 0x1p-1000);
+                       /* underflow */
+                       STRICT_ASSIGN(double, x, 0x1p-1000 * 0x1p-1000);
                        return x;
                }
        }
 
        /* argument reduction */
        if (hx > 0x3fd62e42) {  /* if |x| > 0.5 ln2 */
-               if (hx < 0x3ff0a2b2)  /* if |x| < 1.5 ln2 */
-                       k = 1 - sign - sign; /* optimization */
-               else
+               if (hx >= 0x3ff0a2b2)  /* if |x| >= 1.5 ln2 */
                        k = (int)(invln2*x + half[sign]);
+               else
+                       k = 1 - sign - sign;
                hi = x - k*ln2hi;  /* k*ln2hi is exact here */
                lo = k*ln2lo;
                STRICT_ASSIGN(double, x, hi - lo);
@@ -124,9 +126,9 @@ double exp(double x)
        }
 
        /* x is now in primary range */
-       z = x*x;
-       c = x - z*(P1+z*(P2+z*(P3+z*(P4+z*P5))));
-       x = 1 + ((x*c/(2-c) - lo) + hi);
+       xx = x*x;
+       c = x - xx*(P1+xx*(P2+xx*(P3+xx*(P4+xx*P5))));
+       x = 1 + (x*c/(2-c) - lo + hi);
        if (k == 0)
                return x;
        return scalbn(x, k);