use __expo2 in sinh and cosh, move __cexp to cmath

[libm] / src / math / __expf.c

diff --git a/src/math/__expf.c b/src/math/__expf.c
index fa4fcdc..192838f 100644 (file)
--- a/src/math/__expf.c
+++ b/src/math/__expf.c
@@ -27,53 +27,25 @@
 
 #include "libm.h"
 
-static const uint32_t k = 235; /* constant for reduction */
-static const float kln2 = 162.88958740F; /* k * ln2 */
-
 /*
- * See __exp.c for details.
- *
- * Input:  ln(FLT_MAX) <= x < ln(2 * FLT_MAX / FLT_MIN_DENORM) ~= 192.7
- * Output: 2**127 <= y < 2**128
+ * We use exp(x) = exp(x - kln2) * 2**k,
+ * k is carefully chosen to minimize |exp(kln2) - 2**k|
  */
-static float __frexp_expf(float x, int *expt)
-{
-       float exp_x;
-       uint32_t hx;
-
-       exp_x = expf(x - kln2);
-       GET_FLOAT_WORD(hx, exp_x);
-       *expt = (hx >> 23) - (0x7f + 127) + k;
-       SET_FLOAT_WORD(exp_x, (hx & 0x7fffff) | ((0x7f + 127) << 23));
-       return exp_x;
-}
-
-float __ldexp_expf(float x, int expt)
-{
-       float exp_x, scale;
-       int ex_expt;
-
-       exp_x = __frexp_expf(x, &ex_expt);
-       expt += ex_expt;
-       SET_FLOAT_WORD(scale, (0x7f + expt) << 23);
-       return exp_x * scale;
-}
+static const uint32_t k = 235;
+static const float kln2 = 162.88958740f;
 
-float complex __ldexp_cexpf(float complex z, int expt)
+/* expf(x)/2 when x is huge */
+float __expo2f(float x)
 {
-       float x, y, exp_x, scale1, scale2;
-       int ex_expt, half_expt;
-
-       x = crealf(z);
-       y = cimagf(z);
-       exp_x = __frexp_expf(x, &ex_expt);
-       expt += ex_expt;
-
-       half_expt = expt / 2;
-       SET_FLOAT_WORD(scale1, (0x7f + half_expt) << 23);
-       half_expt = expt - half_expt;
-       SET_FLOAT_WORD(scale2, (0x7f + half_expt) << 23);
-
-       return (cpackf(cosf(y) * exp_x * scale1 * scale2,
-               sinf(y) * exp_x * scale1 * scale2));
+       float scale;
+       int n;
+
+       /*
+        * efficient scalbnf(y, k-1):
+        * 2**(k-1) cannot be represented
+        * so we use that k-1 is even and scale in two steps
+        */
+       n = (k - 1)/2;
+       SET_FLOAT_WORD(scale, (0x7f + n) << 23);
+       return expf(x - kln2) * scale * scale;
 }