summaryrefslogtreecommitdiff
path: root/sysdeps/ieee754/dbl-64/e_log.c
diff options
context:
space:
mode:
Diffstat (limited to 'sysdeps/ieee754/dbl-64/e_log.c')
-rw-r--r--sysdeps/ieee754/dbl-64/e_log.c129
1 files changed, 17 insertions, 112 deletions
diff --git a/sysdeps/ieee754/dbl-64/e_log.c b/sysdeps/ieee754/dbl-64/e_log.c
index 9917dc236f..2483dd8551 100644
--- a/sysdeps/ieee754/dbl-64/e_log.c
+++ b/sysdeps/ieee754/dbl-64/e_log.c
@@ -1,7 +1,7 @@
/*
* IBM Accurate Mathematical Library
* written by International Business Machines Corp.
- * Copyright (C) 2001-2016 Free Software Foundation, Inc.
+ * Copyright (C) 2001-2018 Free Software Foundation, Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
@@ -23,11 +23,10 @@
/* FUNCTION:ulog */
/* */
/* FILES NEEDED: dla.h endian.h mpa.h mydefs.h ulog.h */
-/* mpexp.c mplog.c mpa.c */
/* ulog.tbl */
/* */
/* An ultimate log routine. Given an IEEE double machine number x */
-/* it computes the correctly rounded (to nearest) value of log(x). */
+/* it computes the rounded (to nearest) value of log(x). */
/* Assumption: Machine arithmetic operations are performed in */
/* round to nearest mode of IEEE 754 standard. */
/* */
@@ -40,34 +39,26 @@
#include "MathLib.h"
#include <math.h>
#include <math_private.h>
-#include <stap-probe.h>
#ifndef SECTION
# define SECTION
#endif
-void __mplog (mp_no *, mp_no *, int);
-
/*********************************************************************/
-/* An ultimate log routine. Given an IEEE double machine number x */
-/* it computes the correctly rounded (to nearest) value of log(x). */
+/* An ultimate log routine. Given an IEEE double machine number x */
+/* it computes the rounded (to nearest) value of log(x). */
/*********************************************************************/
double
SECTION
__ieee754_log (double x)
{
-#define M 4
- static const int pr[M] = { 8, 10, 18, 32 };
- int i, j, n, ux, dx, p;
+ int i, j, n, ux, dx;
double dbl_n, u, p0, q, r0, w, nln2a, luai, lubi, lvaj, lvbj,
- sij, ssij, ttij, A, B, B0, y, y1, y2, polI, polII, sa, sb,
- t1, t2, t7, t8, t, ra, rb, ww,
- a0, aa0, s1, s2, ss2, s3, ss3, a1, aa1, a, aa, b, bb, c;
+ sij, ssij, ttij, A, B, B0, polI, polII, t8, a, aa, b, bb, c;
#ifndef DLA_FMS
- double t3, t4, t5, t6;
+ double t1, t2, t3, t4, t5;
#endif
number num;
- mp_no mpx, mpy, mpy1, mpy2, mperr;
#include "ulog.tbl"
#include "ulog.h"
@@ -101,7 +92,7 @@ __ieee754_log (double x)
if (w == 0.0)
return 0.0;
- /*--- Stage I, the case abs(x-1) < 0.03 */
+ /*--- The case abs(x-1) < 0.03 */
t8 = MHALF * w;
EMULV (t8, w, a, aa, t1, t2, t3, t4, t5);
@@ -118,50 +109,12 @@ __ieee754_log (double x)
polII *= w * w * w;
c = (aa + bb) + polII;
- /* End stage I, case abs(x-1) < 0.03 */
- if ((y = b + (c + b * E2)) == b + (c - b * E2))
- return y;
-
- /*--- Stage II, the case abs(x-1) < 0.03 */
-
- a = d19.d + w * d20.d;
- a = d18.d + w * a;
- a = d17.d + w * a;
- a = d16.d + w * a;
- a = d15.d + w * a;
- a = d14.d + w * a;
- a = d13.d + w * a;
- a = d12.d + w * a;
- a = d11.d + w * a;
-
- EMULV (w, a, s2, ss2, t1, t2, t3, t4, t5);
- ADD2 (d10.d, dd10.d, s2, ss2, s3, ss3, t1, t2);
- MUL2 (w, 0, s3, ss3, s2, ss2, t1, t2, t3, t4, t5, t6, t7, t8);
- ADD2 (d9.d, dd9.d, s2, ss2, s3, ss3, t1, t2);
- MUL2 (w, 0, s3, ss3, s2, ss2, t1, t2, t3, t4, t5, t6, t7, t8);
- ADD2 (d8.d, dd8.d, s2, ss2, s3, ss3, t1, t2);
- MUL2 (w, 0, s3, ss3, s2, ss2, t1, t2, t3, t4, t5, t6, t7, t8);
- ADD2 (d7.d, dd7.d, s2, ss2, s3, ss3, t1, t2);
- MUL2 (w, 0, s3, ss3, s2, ss2, t1, t2, t3, t4, t5, t6, t7, t8);
- ADD2 (d6.d, dd6.d, s2, ss2, s3, ss3, t1, t2);
- MUL2 (w, 0, s3, ss3, s2, ss2, t1, t2, t3, t4, t5, t6, t7, t8);
- ADD2 (d5.d, dd5.d, s2, ss2, s3, ss3, t1, t2);
- MUL2 (w, 0, s3, ss3, s2, ss2, t1, t2, t3, t4, t5, t6, t7, t8);
- ADD2 (d4.d, dd4.d, s2, ss2, s3, ss3, t1, t2);
- MUL2 (w, 0, s3, ss3, s2, ss2, t1, t2, t3, t4, t5, t6, t7, t8);
- ADD2 (d3.d, dd3.d, s2, ss2, s3, ss3, t1, t2);
- MUL2 (w, 0, s3, ss3, s2, ss2, t1, t2, t3, t4, t5, t6, t7, t8);
- ADD2 (d2.d, dd2.d, s2, ss2, s3, ss3, t1, t2);
- MUL2 (w, 0, s3, ss3, s2, ss2, t1, t2, t3, t4, t5, t6, t7, t8);
- MUL2 (w, 0, s2, ss2, s3, ss3, t1, t2, t3, t4, t5, t6, t7, t8);
- ADD2 (w, 0, s3, ss3, b, bb, t1, t2);
+ /* Here b contains the high part of the result, and c the low part.
+ Maximum error is b * 2.334e-19, so accuracy is >61 bits.
+ Therefore max ULP error of b + c is ~0.502. */
+ return b + c;
- /* End stage II, case abs(x-1) < 0.03 */
- if ((y = b + (bb + b * E4)) == b + (bb - b * E4))
- return y;
- goto stage_n;
-
- /*--- Stage I, the case abs(x-1) > 0.03 */
+ /*--- The case abs(x-1) > 0.03 */
case_03:
/* Find n,u such that x = u*2**n, 1/sqrt(2) < u < sqrt(2) */
@@ -203,58 +156,10 @@ case_03:
B0 = (((lubi + lvbj) + ssij) + ttij) + dbl_n * LN2B;
B = polI + B0;
- /* End stage I, case abs(x-1) >= 0.03 */
- if ((y = A + (B + E1)) == A + (B - E1))
- return y;
-
-
- /*--- Stage II, the case abs(x-1) > 0.03 */
-
- /* Improve the accuracy of r0 */
- EMULV (p0, r0, sa, sb, t1, t2, t3, t4, t5);
- t = r0 * ((1 - sa) - sb);
- EADD (r0, t, ra, rb);
-
- /* Compute w */
- MUL2 (q, 0, ra, rb, w, ww, t1, t2, t3, t4, t5, t6, t7, t8);
-
- EADD (A, B0, a0, aa0);
-
- /* Evaluate polynomial III */
- s1 = (c3.d + (c4.d + c5.d * w) * w) * w;
- EADD (c2.d, s1, s2, ss2);
- MUL2 (s2, ss2, w, ww, s3, ss3, t1, t2, t3, t4, t5, t6, t7, t8);
- MUL2 (s3, ss3, w, ww, s2, ss2, t1, t2, t3, t4, t5, t6, t7, t8);
- ADD2 (s2, ss2, w, ww, s3, ss3, t1, t2);
- ADD2 (s3, ss3, a0, aa0, a1, aa1, t1, t2);
-
- /* End stage II, case abs(x-1) >= 0.03 */
- if ((y = a1 + (aa1 + E3)) == a1 + (aa1 - E3))
- return y;
-
-
- /* Final stages. Use multi-precision arithmetic. */
-stage_n:
-
- for (i = 0; i < M; i++)
- {
- p = pr[i];
- __dbl_mp (x, &mpx, p);
- __dbl_mp (y, &mpy, p);
- __mplog (&mpx, &mpy, p);
- __dbl_mp (e[i].d, &mperr, p);
- __add (&mpy, &mperr, &mpy1, p);
- __sub (&mpy, &mperr, &mpy2, p);
- __mp_dbl (&mpy1, &y1, p);
- __mp_dbl (&mpy2, &y2, p);
- if (y1 == y2)
- {
- LIBC_PROBE (slowlog, 3, &p, &x, &y1);
- return y1;
- }
- }
- LIBC_PROBE (slowlog_inexact, 3, &p, &x, &y1);
- return y1;
+ /* Here A contains the high part of the result, and B the low part.
+ Maximum abs error is 6.095e-21 and min log (x) is 0.0295 since x > 1.03.
+ Therefore max ULP error of A + B is ~0.502. */
+ return A + B;
}
#ifndef __ieee754_log
generated by cgit v1.2.3 (git 2.39.1) at 2024-04-30 09:58:39 +0000