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authorSzabolcs Nagy <nsz@port70.net>2012-11-17 23:39:39 +0100
committerSzabolcs Nagy <nsz@port70.net>2012-11-17 23:39:39 +0100
commit159c7655d06f04aa56a57385d633699c4c63d72c (patch)
tree793f956303959e9dc6086099571908014dd33b5d /src/math/exp2l.c
parentbbbf045ce96fe5daae7e220487dc44c9d971bd9d (diff)
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math: cleanup exp2.c exp2f.c and exp2l.c
* old code relied on sign extension on right shift * exp2l ld64 wrapper was wrong * use scalbn instead of bithacks
Diffstat (limited to 'src/math/exp2l.c')
-rw-r--r--src/math/exp2l.c59
1 files changed, 20 insertions, 39 deletions
diff --git a/src/math/exp2l.c b/src/math/exp2l.c
index b587308f..145c20fe 100644
--- a/src/math/exp2l.c
+++ b/src/math/exp2l.c
@@ -30,7 +30,7 @@
#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
long double exp2l(long double x)
{
- return exp2l(x);
+ return exp2(x);
}
#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
@@ -40,10 +40,6 @@ long double exp2l(long double x)
#define BIAS (LDBL_MAX_EXP - 1)
#define EXPMASK (BIAS + LDBL_MAX_EXP)
-static const long double huge = 0x1p10000L;
-/* XXX Prevent gcc from erroneously constant folding this. */
-static const volatile long double twom10000 = 0x1p-10000L;
-
static const double
redux = 0x1.8p63 / TBLSIZE,
P1 = 0x1.62e42fefa39efp-1,
@@ -208,27 +204,28 @@ static const double tbl[TBLSIZE * 2] = {
long double exp2l(long double x)
{
union IEEEl2bits u, v;
- long double r, twopk, twopkp10000, z;
+ long double r, z;
uint32_t hx, ix, i0;
- int k;
+ union {uint32_t u; int32_t i;} k;
/* Filter out exceptional cases. */
u.e = x;
hx = u.xbits.expsign;
ix = hx & EXPMASK;
if (ix >= BIAS + 14) { /* |x| >= 16384 or x is NaN */
- if (ix == BIAS + LDBL_MAX_EXP) {
- if (u.xbits.man != 1ULL << 63 || (hx & 0x8000) == 0)
- return x + x; /* x is +Inf or NaN */
- return 0.0; /* x is -Inf */
+ if (ix == EXPMASK) {
+ if (u.xbits.man == 1ULL << 63 && hx == 0xffff) /* -inf */
+ return 0;
+ return x;
+ }
+ if (x >= 16384) {
+ x *= 0x1p16383L;
+ return x;
}
- if (x >= 16384)
- return huge * huge; /* overflow */
if (x <= -16446)
- return twom10000 * twom10000; /* underflow */
- } else if (ix <= BIAS - 66) { /* |x| < 0x1p-66 */
- return 1.0 + x;
- }
+ return 0x1p-10000L*0x1p-10000L;
+ } else if (ix < BIAS - 64) /* |x| < 0x1p-64 */
+ return 1 + x;
/*
* Reduce x, computing z, i0, and k. The low bits of x + redux
@@ -240,38 +237,22 @@ long double exp2l(long double x)
* Then the low-order word of x + redux is 0x000abc12,
* We split this into k = 0xabc and i0 = 0x12 (adjusted to
* index into the table), then we compute z = 0x0.003456p0.
- *
- * XXX If the exponent is negative, the computation of k depends on
- * '>>' doing sign extension.
*/
u.e = x + redux;
i0 = u.bits.manl + TBLSIZE / 2;
- k = (int)i0 >> TBLBITS;
- i0 = (i0 & (TBLSIZE - 1)) << 1;
+ k.u = i0 / TBLSIZE * TBLSIZE;
+ k.i /= TBLSIZE;
+ i0 %= TBLSIZE;
u.e -= redux;
z = x - u.e;
- v.xbits.man = 1ULL << 63;
- if (k >= LDBL_MIN_EXP) {
- v.xbits.expsign = LDBL_MAX_EXP - 1 + k;
- twopk = v.e;
- } else {
- v.xbits.expsign = LDBL_MAX_EXP - 1 + k + 10000;
- twopkp10000 = v.e;
- }
/* Compute r = exp2l(y) = exp2lt[i0] * p(z). */
- long double t_hi = tbl[i0];
- long double t_lo = tbl[i0 + 1];
+ long double t_hi = tbl[2*i0];
+ long double t_lo = tbl[2*i0 + 1];
/* XXX This gives > 1 ulp errors outside of FE_TONEAREST mode */
r = t_lo + (t_hi + t_lo) * z * (P1 + z * (P2 + z * (P3 + z * (P4
+ z * (P5 + z * P6))))) + t_hi;
- /* Scale by 2**k. */
- if (k >= LDBL_MIN_EXP) {
- if (k == LDBL_MAX_EXP)
- return r * 2.0 * 0x1p16383L;
- return r * twopk;
- }
- return r * twopkp10000 * twom10000;
+ return scalbnl(r, k.i);
}
#endif