math: cleanup exp2.c exp2f.c and exp2l.c

[musl] / src / math / exp2.c

diff --git a/src/math/exp2.c b/src/math/exp2.c
index 08c21a6..8e25228 100644 (file)
--- a/src/math/exp2.c
+++ b/src/math/exp2.c
@@ -27,11 +27,9 @@
 
 #include "libm.h"
 
-#define TBLBITS 8
-#define TBLSIZE (1 << TBLBITS)
+#define TBLSIZE 256
 
 static const double
-huge  = 0x1p1000,
 redux = 0x1.8p52 / TBLSIZE,
 P1    = 0x1.62e42fefa39efp-1,
 P2    = 0x1.ebfbdff82c575p-3,
@@ -39,8 +37,6 @@ P3    = 0x1.c6b08d704a0a6p-5,
 P4    = 0x1.3b2ab88f70400p-7,
 P5    = 0x1.5d88003875c74p-10;
 
-static const volatile double twom1000 = 0x1p-1000;
-
 static const double tbl[TBLSIZE * 2] = {
 /*  exp2(z + eps)          eps     */
   0x1.6a09e667f3d5dp-1,  0x1.9880p-44,
@@ -334,25 +330,28 @@ static const double tbl[TBLSIZE * 2] = {
  */
 double exp2(double x)
 {
-       double r, t, twopk, twopkp1000, z;
-       uint32_t hx, ix, lx, i0;
-       int k;
+       double r, t, z;
+       uint32_t hx, ix, i0;
+       union {uint32_t u; int32_t i;} k;
 
        /* Filter out exceptional cases. */
        GET_HIGH_WORD(hx, x);
        ix = hx & 0x7fffffff;
        if (ix >= 0x40900000) {        /* |x| >= 1024 */
                if (ix >= 0x7ff00000) {
-                       GET_LOW_WORD(lx, x);
-                       if (((ix & 0xfffff) | lx) != 0 || (hx & 0x80000000) == 0)
-                               return x + x; /* x is NaN or +Inf */
-                       else
-                               return 0.0;   /* x is -Inf */
+                       GET_LOW_WORD(ix, x);
+                       if (hx == 0xfff00000 && ix == 0) /* -inf */
+                               return 0;
+                       return x;
+               }
+               if (x >= 1024) {
+                       STRICT_ASSIGN(double, x, x * 0x1p1023);
+                       return x;
+               }
+               if (x <= -1075) {
+                       STRICT_ASSIGN(double, x, 0x1p-1000*0x1p-1000);
+                       return x;
                }
-               if (x >= 0x1.0p10)
-                       return huge * huge; /* overflow */
-               if (x <= -0x1.0ccp10)
-                       return twom1000 * twom1000; /* underflow */
        } else if (ix < 0x3c900000) {  /* |x| < 0x1p-54 */
                return 1.0 + x;
        }
@@ -361,24 +360,16 @@ double exp2(double x)
        STRICT_ASSIGN(double, t, x + redux);
        GET_LOW_WORD(i0, t);
        i0 += TBLSIZE / 2;
-       k = (i0 >> TBLBITS) << 20;
-       i0 = (i0 & (TBLSIZE - 1)) << 1;
+       k.u = i0 / TBLSIZE * TBLSIZE;
+       k.i /= TBLSIZE;
+       i0 %= TBLSIZE;
        t -= redux;
        z = x - t;
 
        /* Compute r = exp2(y) = exp2t[i0] * p(z - eps[i]). */
-       t = tbl[i0];       /* exp2t[i0] */
-       z -= tbl[i0 + 1];  /* eps[i0]   */
-       if (k >= -1021 << 20)
-               INSERT_WORDS(twopk, 0x3ff00000 + k, 0);
-       else
-               INSERT_WORDS(twopkp1000, 0x3ff00000 + k + (1000 << 20), 0);
+       t = tbl[2*i0];       /* exp2t[i0] */
+       z -= tbl[2*i0 + 1];  /* eps[i0]   */
        r = t + t * z * (P1 + z * (P2 + z * (P3 + z * (P4 + z * P5))));
 
-       /* Scale by 2**(k>>20). */
-       if (k < -1021 << 20)
-               return r * twopkp1000 * twom1000;
-       if (k == 1024 << 20)
-               return r * 2.0 * 0x1p1023;
-       return r * twopk;
+       return scalbn(r, k.i);
 }