-/* origin: FreeBSD /usr/src/lib/msun/src/e_powf.c */
/*
- * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
- */
-/*
- * ====================================================
- * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
- *
- * Developed at SunPro, a Sun Microsystems, Inc. business.
- * Permission to use, copy, modify, and distribute this
- * software is freely granted, provided that this notice
- * is preserved.
- * ====================================================
+ * Copyright (c) 2017-2018, Arm Limited.
+ * SPDX-License-Identifier: MIT
*/
+#include <math.h>
+#include <stdint.h>
#include "libm.h"
+#include "exp2f_data.h"
+#include "powf_data.h"
-static const float
-bp[] = {1.0, 1.5,},
-dp_h[] = { 0.0, 5.84960938e-01,}, /* 0x3f15c000 */
-dp_l[] = { 0.0, 1.56322085e-06,}, /* 0x35d1cfdc */
-two24 = 16777216.0, /* 0x4b800000 */
-huge = 1.0e30,
-tiny = 1.0e-30,
-/* poly coefs for (3/2)*(log(x)-2s-2/3*s**3 */
-L1 = 6.0000002384e-01, /* 0x3f19999a */
-L2 = 4.2857143283e-01, /* 0x3edb6db7 */
-L3 = 3.3333334327e-01, /* 0x3eaaaaab */
-L4 = 2.7272811532e-01, /* 0x3e8ba305 */
-L5 = 2.3066075146e-01, /* 0x3e6c3255 */
-L6 = 2.0697501302e-01, /* 0x3e53f142 */
-P1 = 1.6666667163e-01, /* 0x3e2aaaab */
-P2 = -2.7777778450e-03, /* 0xbb360b61 */
-P3 = 6.6137559770e-05, /* 0x388ab355 */
-P4 = -1.6533901999e-06, /* 0xb5ddea0e */
-P5 = 4.1381369442e-08, /* 0x3331bb4c */
-lg2 = 6.9314718246e-01, /* 0x3f317218 */
-lg2_h = 6.93145752e-01, /* 0x3f317200 */
-lg2_l = 1.42860654e-06, /* 0x35bfbe8c */
-ovt = 4.2995665694e-08, /* -(128-log2(ovfl+.5ulp)) */
-cp = 9.6179670095e-01, /* 0x3f76384f =2/(3ln2) */
-cp_h = 9.6191406250e-01, /* 0x3f764000 =12b cp */
-cp_l = -1.1736857402e-04, /* 0xb8f623c6 =tail of cp_h */
-ivln2 = 1.4426950216e+00, /* 0x3fb8aa3b =1/ln2 */
-ivln2_h = 1.4426879883e+00, /* 0x3fb8aa00 =16b 1/ln2*/
-ivln2_l = 7.0526075433e-06; /* 0x36eca570 =1/ln2 tail*/
+/*
+POWF_LOG2_POLY_ORDER = 5
+EXP2F_TABLE_BITS = 5
-float powf(float x, float y)
+ULP error: 0.82 (~ 0.5 + relerr*2^24)
+relerr: 1.27 * 2^-26 (Relative error ~= 128*Ln2*relerr_log2 + relerr_exp2)
+relerr_log2: 1.83 * 2^-33 (Relative error of logx.)
+relerr_exp2: 1.69 * 2^-34 (Relative error of exp2(ylogx).)
+*/
+
+#define N (1 << POWF_LOG2_TABLE_BITS)
+#define T __powf_log2_data.tab
+#define A __powf_log2_data.poly
+#define OFF 0x3f330000
+
+/* Subnormal input is normalized so ix has negative biased exponent.
+ Output is multiplied by N (POWF_SCALE) if TOINT_INTRINICS is set. */
+static inline double_t log2_inline(uint32_t ix)
{
- float z,ax,z_h,z_l,p_h,p_l;
- float y1,t1,t2,r,s,sn,t,u,v,w;
- int32_t i,j,k,yisint,n;
- int32_t hx,hy,ix,iy,is;
+ double_t z, r, r2, r4, p, q, y, y0, invc, logc;
+ uint32_t iz, top, tmp;
+ int k, i;
- GET_FLOAT_WORD(hx, x);
- GET_FLOAT_WORD(hy, y);
- ix = hx & 0x7fffffff;
- iy = hy & 0x7fffffff;
+ /* x = 2^k z; where z is in range [OFF,2*OFF] and exact.
+ The range is split into N subintervals.
+ The ith subinterval contains z and c is near its center. */
+ tmp = ix - OFF;
+ i = (tmp >> (23 - POWF_LOG2_TABLE_BITS)) % N;
+ top = tmp & 0xff800000;
+ iz = ix - top;
+ k = (int32_t)top >> (23 - POWF_SCALE_BITS); /* arithmetic shift */
+ invc = T[i].invc;
+ logc = T[i].logc;
+ z = (double_t)asfloat(iz);
- /* x**0 = 1, even if x is NaN */
- if (iy == 0)
- return 1.0f;
- /* 1**y = 1, even if y is NaN */
- if (hx == 0x3f800000)
- return 1.0f;
- /* NaN if either arg is NaN */
- if (ix > 0x7f800000 || iy > 0x7f800000)
- return x + y;
+ /* log2(x) = log1p(z/c-1)/ln2 + log2(c) + k */
+ r = z * invc - 1;
+ y0 = logc + (double_t)k;
- /* determine if y is an odd int when x < 0
- * yisint = 0 ... y is not an integer
- * yisint = 1 ... y is an odd int
- * yisint = 2 ... y is an even int
- */
- yisint = 0;
- if (hx < 0) {
- if (iy >= 0x4b800000)
- yisint = 2; /* even integer y */
- else if (iy >= 0x3f800000) {
- k = (iy>>23) - 0x7f; /* exponent */
- j = iy>>(23-k);
- if ((j<<(23-k)) == iy)
- yisint = 2 - (j & 1);
- }
- }
+ /* Pipelined polynomial evaluation to approximate log1p(r)/ln2. */
+ r2 = r * r;
+ y = A[0] * r + A[1];
+ p = A[2] * r + A[3];
+ r4 = r2 * r2;
+ q = A[4] * r + y0;
+ q = p * r2 + q;
+ y = y * r4 + q;
+ return y;
+}
- /* special value of y */
- if (iy == 0x7f800000) { /* y is +-inf */
- if (ix == 0x3f800000) /* (-1)**+-inf is 1 */
- return 1.0f;
- else if (ix > 0x3f800000) /* (|x|>1)**+-inf = inf,0 */
- return hy >= 0 ? y : 0.0f;
- else /* (|x|<1)**+-inf = 0,inf */
- return hy >= 0 ? 0.0f: -y;
- }
- if (iy == 0x3f800000) /* y is +-1 */
- return hy >= 0 ? x : 1.0f/x;
- if (hy == 0x40000000) /* y is 2 */
- return x*x;
- if (hy == 0x3f000000) { /* y is 0.5 */
- if (hx >= 0) /* x >= +0 */
- return sqrtf(x);
- }
+#undef N
+#undef T
+#define N (1 << EXP2F_TABLE_BITS)
+#define T __exp2f_data.tab
+#define SIGN_BIAS (1 << (EXP2F_TABLE_BITS + 11))
- ax = fabsf(x);
- /* special value of x */
- if (ix == 0x7f800000 || ix == 0 || ix == 0x3f800000) { /* x is +-0,+-inf,+-1 */
- z = ax;
- if (hy < 0) /* z = (1/|x|) */
- z = 1.0f/z;
- if (hx < 0) {
- if (((ix-0x3f800000)|yisint) == 0) {
- z = (z-z)/(z-z); /* (-1)**non-int is NaN */
- } else if (yisint == 1)
- z = -z; /* (x<0)**odd = -(|x|**odd) */
- }
- return z;
- }
+/* The output of log2 and thus the input of exp2 is either scaled by N
+ (in case of fast toint intrinsics) or not. The unscaled xd must be
+ in [-1021,1023], sign_bias sets the sign of the result. */
+static inline float exp2_inline(double_t xd, uint32_t sign_bias)
+{
+ uint64_t ki, ski, t;
+ double_t kd, z, r, r2, y, s;
- sn = 1.0f; /* sign of result */
- if (hx < 0) {
- if (yisint == 0) /* (x<0)**(non-int) is NaN */
- return (x-x)/(x-x);
- if (yisint == 1) /* (x<0)**(odd int) */
- sn = -1.0f;
- }
+#if TOINT_INTRINSICS
+#define C __exp2f_data.poly_scaled
+ /* N*x = k + r with r in [-1/2, 1/2] */
+ kd = roundtoint(xd); /* k */
+ ki = converttoint(xd);
+#else
+#define C __exp2f_data.poly
+#define SHIFT __exp2f_data.shift_scaled
+ /* x = k/N + r with r in [-1/(2N), 1/(2N)] */
+ kd = eval_as_double(xd + SHIFT);
+ ki = asuint64(kd);
+ kd -= SHIFT; /* k/N */
+#endif
+ r = xd - kd;
- /* |y| is huge */
- if (iy > 0x4d000000) { /* if |y| > 2**27 */
- /* over/underflow if x is not close to one */
- if (ix < 0x3f7ffff8)
- return hy < 0 ? sn*huge*huge : sn*tiny*tiny;
- if (ix > 0x3f800007)
- return hy > 0 ? sn*huge*huge : sn*tiny*tiny;
- /* now |1-x| is tiny <= 2**-20, suffice to compute
- log(x) by x-x^2/2+x^3/3-x^4/4 */
- t = ax - 1; /* t has 20 trailing zeros */
- w = (t*t)*(0.5f - t*(0.333333333333f - t*0.25f));
- u = ivln2_h*t; /* ivln2_h has 16 sig. bits */
- v = t*ivln2_l - w*ivln2;
- t1 = u + v;
- GET_FLOAT_WORD(is, t1);
- SET_FLOAT_WORD(t1, is & 0xfffff000);
- t2 = v - (t1-u);
- } else {
- float s2,s_h,s_l,t_h,t_l;
- n = 0;
- /* take care subnormal number */
- if (ix < 0x00800000) {
- ax *= two24;
- n -= 24;
- GET_FLOAT_WORD(ix, ax);
- }
- n += ((ix)>>23) - 0x7f;
- j = ix & 0x007fffff;
- /* determine interval */
- ix = j | 0x3f800000; /* normalize ix */
- if (j <= 0x1cc471) /* |x|<sqrt(3/2) */
- k = 0;
- else if (j < 0x5db3d7) /* |x|<sqrt(3) */
- k = 1;
- else {
- k = 0;
- n += 1;
- ix -= 0x00800000;
- }
- SET_FLOAT_WORD(ax, ix);
+ /* exp2(x) = 2^(k/N) * 2^r ~= s * (C0*r^3 + C1*r^2 + C2*r + 1) */
+ t = T[ki % N];
+ ski = ki + sign_bias;
+ t += ski << (52 - EXP2F_TABLE_BITS);
+ s = asdouble(t);
+ z = C[0] * r + C[1];
+ r2 = r * r;
+ y = C[2] * r + 1;
+ y = z * r2 + y;
+ y = y * s;
+ return eval_as_float(y);
+}
- /* compute s = s_h+s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5) */
- u = ax - bp[k]; /* bp[0]=1.0, bp[1]=1.5 */
- v = 1.0f/(ax+bp[k]);
- s = u*v;
- s_h = s;
- GET_FLOAT_WORD(is, s_h);
- SET_FLOAT_WORD(s_h, is & 0xfffff000);
- /* t_h=ax+bp[k] High */
- is = ((ix>>1) & 0xfffff000) | 0x20000000;
- SET_FLOAT_WORD(t_h, is + 0x00400000 + (k<<21));
- t_l = ax - (t_h - bp[k]);
- s_l = v*((u - s_h*t_h) - s_h*t_l);
- /* compute log(ax) */
- s2 = s*s;
- r = s2*s2*(L1+s2*(L2+s2*(L3+s2*(L4+s2*(L5+s2*L6)))));
- r += s_l*(s_h+s);
- s2 = s_h*s_h;
- t_h = 3.0f + s2 + r;
- GET_FLOAT_WORD(is, t_h);
- SET_FLOAT_WORD(t_h, is & 0xfffff000);
- t_l = r - ((t_h - 3.0f) - s2);
- /* u+v = s*(1+...) */
- u = s_h*t_h;
- v = s_l*t_h + t_l*s;
- /* 2/(3log2)*(s+...) */
- p_h = u + v;
- GET_FLOAT_WORD(is, p_h);
- SET_FLOAT_WORD(p_h, is & 0xfffff000);
- p_l = v - (p_h - u);
- z_h = cp_h*p_h; /* cp_h+cp_l = 2/(3*log2) */
- z_l = cp_l*p_h + p_l*cp+dp_l[k];
- /* log2(ax) = (s+..)*2/(3*log2) = n + dp_h + z_h + z_l */
- t = (float)n;
- t1 = (((z_h + z_l) + dp_h[k]) + t);
- GET_FLOAT_WORD(is, t1);
- SET_FLOAT_WORD(t1, is & 0xfffff000);
- t2 = z_l - (((t1 - t) - dp_h[k]) - z_h);
- }
+/* Returns 0 if not int, 1 if odd int, 2 if even int. The argument is
+ the bit representation of a non-zero finite floating-point value. */
+static inline int checkint(uint32_t iy)
+{
+ int e = iy >> 23 & 0xff;
+ if (e < 0x7f)
+ return 0;
+ if (e > 0x7f + 23)
+ return 2;
+ if (iy & ((1 << (0x7f + 23 - e)) - 1))
+ return 0;
+ if (iy & (1 << (0x7f + 23 - e)))
+ return 1;
+ return 2;
+}
+
+static inline int zeroinfnan(uint32_t ix)
+{
+ return 2 * ix - 1 >= 2u * 0x7f800000 - 1;
+}
- /* split up y into y1+y2 and compute (y1+y2)*(t1+t2) */
- GET_FLOAT_WORD(is, y);
- SET_FLOAT_WORD(y1, is & 0xfffff000);
- p_l = (y-y1)*t1 + y*t2;
- p_h = y1*t1;
- z = p_l + p_h;
- GET_FLOAT_WORD(j, z);
- if (j > 0x43000000) /* if z > 128 */
- return sn*huge*huge; /* overflow */
- else if (j == 0x43000000) { /* if z == 128 */
- if (p_l + ovt > z - p_h)
- return sn*huge*huge; /* overflow */
- } else if ((j&0x7fffffff) > 0x43160000) /* z < -150 */ // FIXME: check should be (uint32_t)j > 0xc3160000
- return sn*tiny*tiny; /* underflow */
- else if (j == 0xc3160000) { /* z == -150 */
- if (p_l <= z-p_h)
- return sn*tiny*tiny; /* underflow */
+float powf(float x, float y)
+{
+ uint32_t sign_bias = 0;
+ uint32_t ix, iy;
+
+ ix = asuint(x);
+ iy = asuint(y);
+ if (predict_false(ix - 0x00800000 >= 0x7f800000 - 0x00800000 ||
+ zeroinfnan(iy))) {
+ /* Either (x < 0x1p-126 or inf or nan) or (y is 0 or inf or nan). */
+ if (predict_false(zeroinfnan(iy))) {
+ if (2 * iy == 0)
+ return issignalingf_inline(x) ? x + y : 1.0f;
+ if (ix == 0x3f800000)
+ return issignalingf_inline(y) ? x + y : 1.0f;
+ if (2 * ix > 2u * 0x7f800000 ||
+ 2 * iy > 2u * 0x7f800000)
+ return x + y;
+ if (2 * ix == 2 * 0x3f800000)
+ return 1.0f;
+ if ((2 * ix < 2 * 0x3f800000) == !(iy & 0x80000000))
+ return 0.0f; /* |x|<1 && y==inf or |x|>1 && y==-inf. */
+ return y * y;
+ }
+ if (predict_false(zeroinfnan(ix))) {
+ float_t x2 = x * x;
+ if (ix & 0x80000000 && checkint(iy) == 1)
+ x2 = -x2;
+ /* Without the barrier some versions of clang hoist the 1/x2 and
+ thus division by zero exception can be signaled spuriously. */
+ return iy & 0x80000000 ? fp_barrierf(1 / x2) : x2;
+ }
+ /* x and y are non-zero finite. */
+ if (ix & 0x80000000) {
+ /* Finite x < 0. */
+ int yint = checkint(iy);
+ if (yint == 0)
+ return __math_invalidf(x);
+ if (yint == 1)
+ sign_bias = SIGN_BIAS;
+ ix &= 0x7fffffff;
+ }
+ if (ix < 0x00800000) {
+ /* Normalize subnormal x so exponent becomes negative. */
+ ix = asuint(x * 0x1p23f);
+ ix &= 0x7fffffff;
+ ix -= 23 << 23;
+ }
}
- /*
- * compute 2**(p_h+p_l)
- */
- i = j & 0x7fffffff;
- k = (i>>23) - 0x7f;
- n = 0;
- if (i > 0x3f000000) { /* if |z| > 0.5, set n = [z+0.5] */
- n = j + (0x00800000>>(k+1));
- k = ((n&0x7fffffff)>>23) - 0x7f; /* new k for n */
- SET_FLOAT_WORD(t, n & ~(0x007fffff>>k));
- n = ((n&0x007fffff)|0x00800000)>>(23-k);
- if (j < 0)
- n = -n;
- p_h -= t;
+ double_t logx = log2_inline(ix);
+ double_t ylogx = y * logx; /* cannot overflow, y is single prec. */
+ if (predict_false((asuint64(ylogx) >> 47 & 0xffff) >=
+ asuint64(126.0 * POWF_SCALE) >> 47)) {
+ /* |y*log(x)| >= 126. */
+ if (ylogx > 0x1.fffffffd1d571p+6 * POWF_SCALE)
+ return __math_oflowf(sign_bias);
+ if (ylogx <= -150.0 * POWF_SCALE)
+ return __math_uflowf(sign_bias);
}
- t = p_l + p_h;
- GET_FLOAT_WORD(is, t);
- SET_FLOAT_WORD(t, is & 0xffff8000);
- u = t*lg2_h;
- v = (p_l-(t-p_h))*lg2 + t*lg2_l;
- z = u + v;
- w = v - (z - u);
- t = z*z;
- t1 = z - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
- r = (z*t1)/(t1-2.0f) - (w+z*w);
- z = 1.0f - (r - z);
- GET_FLOAT_WORD(j, z);
- j += n<<23;
- if ((j>>23) <= 0) /* subnormal output */
- z = scalbnf(z, n);
- else
- SET_FLOAT_WORD(z, j);
- return sn*z;
+ return exp2_inline(ylogx, sign_bias);
}
projects / oweals / musl.git / commitdiff