diff options
Diffstat (limited to 'src/math/exp2f.c')
| -rw-r--r-- | src/math/exp2f.c | 52 |
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; } |