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authorSzabolcs Nagy <nsz@port70.net>2013-09-04 07:51:11 +0000
committerSzabolcs Nagy <nsz@port70.net>2013-09-05 11:30:08 +0000
commit39c910fb061114e6aa5c3bf2c94b1d7262d62221 (patch)
tree5ca9b82746e8ac224f93dcda1b8d19f95b68eda2 /src/math/exp2f.c
parentea9bb95a5b36c0a3d2ed8fb03808745b406c2633 (diff)
downloadmusl-39c910fb061114e6aa5c3bf2c94b1d7262d62221.tar.gz
math: fix underflow in exp*.c and long double handling in exp2l
* don't care about inexact flag * use double_t and float_t (faster, smaller, more precise on x86) * exp: underflow when result is zero or subnormal and not -inf * exp2: underflow when result is zero or subnormal and not exact * expm1: underflow when result is zero or subnormal * expl: don't underflow on -inf * exp2: fix incorrect comment * expm1: simplify special case handling and overflow properly * expm1: cleanup final scaling and fix negative left shift ub (twopk)
Diffstat (limited to 'src/math/exp2f.c')
-rw-r--r--src/math/exp2f.c52
1 files changed, 24 insertions, 28 deletions
diff --git a/src/math/exp2f.c b/src/math/exp2f.c
index ea50db4a..91738f04 100644
--- a/src/math/exp2f.c
+++ b/src/math/exp2f.c
@@ -63,7 +63,7 @@ static const double exp2ft[TBLSIZE] = {
* Method: (equally-spaced tables)
*
* Reduce x:
- * x = 2**k + y, for integer k and |y| <= 1/2.
+ * x = k + y, for integer k and |y| <= 1/2.
* Thus we have exp2f(x) = 2**k * exp2(y).
*
* Reduce y:
@@ -83,46 +83,42 @@ static const double exp2ft[TBLSIZE] = {
*/
float exp2f(float x)
{
- double tv, twopk, u, z;
- float t;
- uint32_t hx, ix, i0, k;
+ double_t t, r, z;
+ union {float f; uint32_t i;} u = {x};
+ union {double f; uint64_t i;} uk;
+ uint32_t ix, i0, k;
/* Filter out exceptional cases. */
- GET_FLOAT_WORD(hx, x);
- ix = hx & 0x7fffffff;
- if (ix >= 0x43000000) { /* |x| >= 128 */
- if (ix >= 0x7f800000) {
- if (hx == 0xff800000) /* -inf */
- return 0;
- return x;
- }
- if (x >= 128) {
+ ix = u.i & 0x7fffffff;
+ if (ix > 0x42fc0000) { /* |x| > 126 */
+ if (u.i >= 0x43000000 && u.i < 0x80000000) { /* x >= 128 */
STRICT_ASSIGN(float, x, x * 0x1p127f);
return x;
}
- if (x <= -150) {
- STRICT_ASSIGN(float, x, 0x1p-100f*0x1p-100f);
- return x;
+ if (u.i >= 0x80000000) { /* x < -126 */
+ if (u.i >= 0xc3160000 || (u.i & 0x0000ffff))
+ FORCE_EVAL(-0x1p-149f/x);
+ if (u.i >= 0xc3160000) /* x <= -150 */
+ return 0;
}
} else if (ix <= 0x33000000) { /* |x| <= 0x1p-25 */
return 1.0f + x;
}
/* Reduce x, computing z, i0, and k. */
- STRICT_ASSIGN(float, t, x + redux);
- GET_FLOAT_WORD(i0, t);
+ u.f = x + redux;
+ i0 = u.i;
i0 += TBLSIZE / 2;
- k = (i0 / TBLSIZE) << 20;
+ k = i0 / TBLSIZE;
+ uk.i = (uint64_t)(0x3ff + k)<<52;
i0 &= TBLSIZE - 1;
- t -= redux;
- z = x - t;
- INSERT_WORDS(twopk, 0x3ff00000 + k, 0);
-
+ u.f -= redux;
+ z = x - u.f;
/* Compute r = exp2(y) = exp2ft[i0] * p(z). */
- tv = exp2ft[i0];
- u = tv * z;
- tv = tv + u * (P1 + z * P2) + u * (z * z) * (P3 + z * P4);
+ r = exp2ft[i0];
+ t = r * z;
+ r = r + t * (P1 + z * P2) + t * (z * z) * (P3 + z * P4);
- /* Scale by 2**(k>>20). */
- return tv * twopk;
+ /* Scale by 2**k */
+ return r * uk.f;
}