Add new log2 implementation

Similar algorithm is used as in log: log2(2^k x) = k + log2(c) + log2(x/c)
where the last term is approximated by a polynomial of x/c - 1, the first
order coefficient is about 1/ln2 in this case.

There is separate code path when fma instruction is not available for
computing x/c - 1 precisely, for which the table size is doubled.

The worst case error is 0.547 ULP (0.55 without fma), the read only
global data size is 1168 bytes (2192 without fma) on aarch64.  The
non-nearest rounding error is less than 1 ULP.

Improvements on Cortex-A72 compared to current glibc master:
log2 thruput: 2.00x in [0.01 11.1]
log2 latency: 2.04x in [0.01 11.1]
log2 thruput: 2.17x in [0.999 1.001]
log2 latency: 2.88x in [0.999 1.001]

Tested on
aarch64-linux-gnu (defined __FP_FAST_FMA)
arm-linux-gnueabihf (!defined __FP_FAST_FMA)
x86_64-linux-gnu (!defined __FP_FAST_FMA)
powerpc64le-linxu-gnu (defined __FP_FAST_FMA)
targets.

	* NEWS: Mention log2 improvements.
	* math/Makefile (type-double-routines): Add e_log2_data.
	* sysdeps/i386/fpu/e_log2_data.c: New file.
	* sysdeps/ia64/fpu/e_log2_data.c: New file.
	* sysdeps/ieee754/dbl-64/e_log2.c: Rewrite.
	* sysdeps/ieee754/dbl-64/e_log2_data.c: New file.
	* sysdeps/ieee754/dbl-64/math_config.h (__log2_data): Add.
	* sysdeps/ieee754/dbl-64/wordsize-64/e_log2.c: Remove.
	* sysdeps/m68k/m680x0/fpu/e_log2_data.c: New file.

10 files changed, 378 insertions, 246 deletions

diff --git a/ChangeLog b/ChangeLog
index 8c990ad7b7..696e456957 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,17 @@
 2018-09-12  Szabolcs Nagy  <szabolcs.nagy@arm.com>
 
+	* NEWS: Mention log2 improvements.
+	* math/Makefile (type-double-routines): Add e_log2_data.
+	* sysdeps/i386/fpu/e_log2_data.c: New file.
+	* sysdeps/ia64/fpu/e_log2_data.c: New file.
+	* sysdeps/ieee754/dbl-64/e_log2.c: Rewrite.
+	* sysdeps/ieee754/dbl-64/e_log2_data.c: New file.
+	* sysdeps/ieee754/dbl-64/math_config.h (__log2_data): Add.
+	* sysdeps/ieee754/dbl-64/wordsize-64/e_log2.c: Remove.
+	* sysdeps/m68k/m680x0/fpu/e_log2_data.c: New file.
+
+2018-09-12  Szabolcs Nagy  <szabolcs.nagy@arm.com>
+
 	* NEWS: Mention log improvement.
 	* math/Makefile (type-double-routines): Add e_log_data.
 	* sysdeps/i386/fpu/e_log_data.c: New file.
diff --git a/NEWS b/NEWS
index 79bee8ee6b..04a0e89010 100644
--- a/NEWS
+++ b/NEWS
@@ -16,7 +16,7 @@ Major new features:
   to set the install root if you wish to install into a non-default
   configured location.
 
-* Optimized generic exp, exp2, log, sinf, cosf, sincosf and tanf.
+* Optimized generic exp, exp2, log, log2, sinf, cosf, sincosf and tanf.
 
 * The reallocarray function is now declared under _DEFAULT_SOURCE, not just
   for _GNU_SOURCE, to match BSD environments.
diff --git a/math/Makefile b/math/Makefile
index 8bfbebc4d0..2537b2a9ad 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -127,7 +127,8 @@ type-ldouble-yes := ldouble
 type-double-suffix :=
 type-double-routines := branred doasin dosincos mpa mpatan2	\
 		       k_rem_pio2 mpatan mpsqrt mptan sincos32	\
-		       sincostab math_err e_exp_data e_log_data
+		       sincostab math_err e_exp_data e_log_data	\
+		       e_log2_data
 
 # float support
 type-float-suffix := f
diff --git a/sysdeps/i386/fpu/e_log2_data.c b/sysdeps/i386/fpu/e_log2_data.c
new file mode 100644
index 0000000000..1cc8931700
--- /dev/null
+++ b/sysdeps/i386/fpu/e_log2_data.c
@@ -0,0 +1 @@
+/* Not needed.  */
diff --git a/sysdeps/ia64/fpu/e_log2_data.c b/sysdeps/ia64/fpu/e_log2_data.c
new file mode 100644
index 0000000000..1cc8931700
--- /dev/null
+++ b/sysdeps/ia64/fpu/e_log2_data.c
@@ -0,0 +1 @@
+/* Not needed.  */
diff --git a/sysdeps/ieee754/dbl-64/e_log2.c b/sysdeps/ieee754/dbl-64/e_log2.c
index e4a6aff9a3..916eb466f8 100644
--- a/sysdeps/ieee754/dbl-64/e_log2.c
+++ b/sysdeps/ieee754/dbl-64/e_log2.c
@@ -1,133 +1,141 @@
-/* Adapted for log2 by Ulrich Drepper <drepper@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.
- * ====================================================
- */
+/* Double-precision log2(x) function.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
 
-/* __ieee754_log2(x)
- * Return the logarithm to base 2 of x
- *
- * Method :
- *   1. Argument Reduction: find k and f such that
- *			x = 2^k * (1+f),
- *	   where  sqrt(2)/2 < 1+f < sqrt(2) .
- *
- *   2. Approximation of log(1+f).
- *	Let s = f/(2+f) ; based on log(1+f) = log(1+s) - log(1-s)
- *		 = 2s + 2/3 s**3 + 2/5 s**5 + .....,
- *		 = 2s + s*R
- *      We use a special Reme algorithm on [0,0.1716] to generate
- *	a polynomial of degree 14 to approximate R The maximum error
- *	of this polynomial approximation is bounded by 2**-58.45. In
- *	other words,
- *			2      4      6      8      10      12      14
- *	    R(z) ~ Lg1*s +Lg2*s +Lg3*s +Lg4*s +Lg5*s  +Lg6*s  +Lg7*s
- *	(the values of Lg1 to Lg7 are listed in the program)
- *	and
- *	    |      2          14          |     -58.45
- *	    | Lg1*s +...+Lg7*s    -  R(z) | <= 2
- *	    |                             |
- *	Note that 2s = f - s*f = f - hfsq + s*hfsq, where hfsq = f*f/2.
- *	In order to guarantee error in log below 1ulp, we compute log
- *	by
- *		log(1+f) = f - s*(f - R)	(if f is not too large)
- *		log(1+f) = f - (hfsq - s*(hfsq+R)).	(better accuracy)
- *
- *	3. Finally,  log(x) = k + log(1+f).
- *			    = k+(f-(hfsq-(s*(hfsq+R))))
- *
- * Special cases:
- *	log2(x) is NaN with signal if x < 0 (including -INF) ;
- *	log2(+INF) is +INF; log(0) is -INF with signal;
- *	log2(NaN) is that NaN with no signal.
- *
- * Constants:
- * The hexadecimal values are the intended ones for the following
- * constants. The decimal values may be used, provided that the
- * compiler will convert from decimal to binary accurately enough
- * to produce the hexadecimal values shown.
- */
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
 
 #include <math.h>
-#include <math_private.h>
-#include <fix-int-fp-convert-zero.h>
+#include <stdint.h>
+#include "math_config.h"
 
-static const double ln2 = 0.69314718055994530942;
-static const double two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */
-static const double Lg1 = 6.666666666666735130e-01;     /* 3FE55555 55555593 */
-static const double Lg2 = 3.999999999940941908e-01;     /* 3FD99999 9997FA04 */
-static const double Lg3 = 2.857142874366239149e-01;     /* 3FD24924 94229359 */
-static const double Lg4 = 2.222219843214978396e-01;     /* 3FCC71C5 1D8E78AF */
-static const double Lg5 = 1.818357216161805012e-01;     /* 3FC74664 96CB03DE */
-static const double Lg6 = 1.531383769920937332e-01;     /* 3FC39A09 D078C69F */
-static const double Lg7 = 1.479819860511658591e-01;     /* 3FC2F112 DF3E5244 */
+#define T __log2_data.tab
+#define T2 __log2_data.tab2
+#define B __log2_data.poly1
+#define A __log2_data.poly
+#define InvLn2hi __log2_data.invln2hi
+#define InvLn2lo __log2_data.invln2lo
+#define N (1 << LOG2_TABLE_BITS)
+#define OFF 0x3fe6000000000000
 
-static const double zero = 0.0;
+/* Top 16 bits of a double.  */
+static inline uint32_t
+top16 (double x)
+{
+  return asuint64 (x) >> 48;
+}
 
 double
 __ieee754_log2 (double x)
 {
-  double hfsq, f, s, z, R, w, t1, t2, dk;
-  int32_t k, hx, i, j;
-  uint32_t lx;
+  /* double_t for better performance on targets with FLT_EVAL_METHOD==2.  */
+  double_t z, r, r2, r4, y, invc, logc, kd, hi, lo, t1, t2, t3, p;
+  uint64_t ix, iz, tmp;
+  uint32_t top;
+  int k, i;
 
-  EXTRACT_WORDS (hx, lx, x);
+  ix = asuint64 (x);
+  top = top16 (x);
 
-  k = 0;
-  if (hx < 0x00100000)
-    {                           /* x < 2**-1022  */
-      if (__glibc_unlikely (((hx & 0x7fffffff) | lx) == 0))
-	return -two54 / fabs (x);        /* log(+-0)=-inf */
-      if (__glibc_unlikely (hx < 0))
-	return (x - x) / (x - x);       /* log(-#) = NaN */
-      k -= 54;
-      x *= two54;               /* subnormal number, scale up x */
-      GET_HIGH_WORD (hx, x);
-    }
-  if (__glibc_unlikely (hx >= 0x7ff00000))
-    return x + x;
-  k += (hx >> 20) - 1023;
-  hx &= 0x000fffff;
-  i = (hx + 0x95f64) & 0x100000;
-  SET_HIGH_WORD (x, hx | (i ^ 0x3ff00000));     /* normalize x or x/2 */
-  k += (i >> 20);
-  dk = (double) k;
-  f = x - 1.0;
-  if ((0x000fffff & (2 + hx)) < 3)
-    {                           /* |f| < 2**-20 */
-      if (f == zero)
-	{
-	  if (FIX_INT_FP_CONVERT_ZERO && dk == 0.0)
-	    dk = 0.0;
-	  return dk;
-	}
-      R = f * f * (0.5 - 0.33333333333333333 * f);
-      return dk - (R - f) / ln2;
-    }
-  s = f / (2.0 + f);
-  z = s * s;
-  i = hx - 0x6147a;
-  w = z * z;
-  j = 0x6b851 - hx;
-  t1 = w * (Lg2 + w * (Lg4 + w * Lg6));
-  t2 = z * (Lg1 + w * (Lg3 + w * (Lg5 + w * Lg7)));
-  i |= j;
-  R = t2 + t1;
-  if (i > 0)
+#define LO asuint64 (1.0 - 0x1.5b51p-5)
+#define HI asuint64 (1.0 + 0x1.6ab2p-5)
+  if (__glibc_unlikely (ix - LO < HI - LO))
     {
-      hfsq = 0.5 * f * f;
-      return dk - ((hfsq - (s * (hfsq + R))) - f) / ln2;
+      /* Handle close to 1.0 inputs separately.  */
+      /* Fix sign of zero with downward rounding when x==1.  */
+      if (WANT_ROUNDING && __glibc_unlikely (ix == asuint64 (1.0)))
+	return 0;
+      r = x - 1.0;
+#ifdef __FP_FAST_FMA
+      hi = r * InvLn2hi;
+      lo = r * InvLn2lo + __builtin_fma (r, InvLn2hi, -hi);
+#else
+      double_t rhi, rlo;
+      rhi = asdouble (asuint64 (r) & -1ULL << 32);
+      rlo = r - rhi;
+      hi = rhi * InvLn2hi;
+      lo = rlo * InvLn2hi + r * InvLn2lo;
+#endif
+      r2 = r * r; /* rounding error: 0x1p-62.  */
+      r4 = r2 * r2;
+      /* Worst-case error is less than 0.54 ULP (0.55 ULP without fma).  */
+      p = r2 * (B[0] + r * B[1]);
+      y = hi + p;
+      lo += hi - y + p;
+      lo += r4 * (B[2] + r * B[3] + r2 * (B[4] + r * B[5])
+		  + r4 * (B[6] + r * B[7] + r2 * (B[8] + r * B[9])));
+      y += lo;
+      return y;
     }
-  else
+  if (__glibc_unlikely (top - 0x0010 >= 0x7ff0 - 0x0010))
     {
-      return dk - ((s * (f - R)) - f) / ln2;
+      /* x < 0x1p-1022 or inf or nan.  */
+      if (ix * 2 == 0)
+	return __math_divzero (1);
+      if (ix == asuint64 (INFINITY)) /* log(inf) == inf.  */
+	return x;
+      if ((top & 0x8000) || (top & 0x7ff0) == 0x7ff0)
+	return __math_invalid (x);
+      /* x is subnormal, normalize it.  */
+      ix = asuint64 (x * 0x1p52);
+      ix -= 52ULL << 52;
     }
-}
 
+  /* 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 >> (52 - LOG2_TABLE_BITS)) % N;
+  k = (int64_t) tmp >> 52; /* arithmetic shift */
+  iz = ix - (tmp & 0xfffULL << 52);
+  invc = T[i].invc;
+  logc = T[i].logc;
+  z = asdouble (iz);
+  kd = (double_t) k;
+
+  /* log2(x) = log2(z/c) + log2(c) + k.  */
+  /* r ~= z/c - 1, |r| < 1/(2*N).  */
+#ifdef __FP_FAST_FMA
+  /* rounding error: 0x1p-55/N.  */
+  r = __builtin_fma (z, invc, -1.0);
+  t1 = r * InvLn2hi;
+  t2 = r * InvLn2lo + __builtin_fma (r, InvLn2hi, -t1);
+#else
+  double_t rhi, rlo;
+  /* rounding error: 0x1p-55/N + 0x1p-65.  */
+  r = (z - T2[i].chi - T2[i].clo) * invc;
+  rhi = asdouble (asuint64 (r) & -1ULL << 32);
+  rlo = r - rhi;
+  t1 = rhi * InvLn2hi;
+  t2 = rlo * InvLn2hi + r * InvLn2lo;
+#endif
+
+  /* hi + lo = r/ln2 + log2(c) + k.  */
+  t3 = kd + logc;
+  hi = t3 + t1;
+  lo = t3 - hi + t1 + t2;
+
+  /* log2(r+1) = r/ln2 + r^2*poly(r).  */
+  /* Evaluation is optimized assuming superscalar pipelined execution.  */
+  r2 = r * r; /* rounding error: 0x1p-54/N^2.  */
+  r4 = r2 * r2;
+  /* Worst-case error if |y| > 0x1p-4: 0.547 ULP (0.550 ULP without fma).
+     ~ 0.5 + 2/N/ln2 + abs-poly-error*0x1p56 ULP (+ 0.003 ULP without fma).  */
+  p = A[0] + r * A[1] + r2 * (A[2] + r * A[3]) + r4 * (A[4] + r * A[5]);
+  y = lo + r2 * p + hi;
+  return y;
+}
+#ifndef __ieee754_log2
 strong_alias (__ieee754_log2, __log2_finite)
+#endif
diff --git a/sysdeps/ieee754/dbl-64/e_log2_data.c b/sysdeps/ieee754/dbl-64/e_log2_data.c
new file mode 100644
index 0000000000..f650072421
--- /dev/null
+++ b/sysdeps/ieee754/dbl-64/e_log2_data.c
@@ -0,0 +1,220 @@
+/* Data for log2.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "math_config.h"
+
+#define N (1 << LOG2_TABLE_BITS)
+
+const struct log2_data __log2_data = {
+// First coefficient: 0x1.71547652b82fe1777d0ffda0d24p0
+.invln2hi = 0x1.7154765200000p+0,
+.invln2lo = 0x1.705fc2eefa200p-33,
+.poly1 = {
+#if LOG2_POLY1_ORDER == 11
+// relative error: 0x1.2fad8188p-63
+// in -0x1.5b51p-5 0x1.6ab2p-5
+-0x1.71547652b82fep-1,
+0x1.ec709dc3a03f7p-2,
+-0x1.71547652b7c3fp-2,
+0x1.2776c50f05be4p-2,
+-0x1.ec709dd768fe5p-3,
+0x1.a61761ec4e736p-3,
+-0x1.7153fbc64a79bp-3,
+0x1.484d154f01b4ap-3,
+-0x1.289e4a72c383cp-3,
+0x1.0b32f285aee66p-3,
+#endif
+},
+.poly = {
+#if N == 64 && LOG2_POLY_ORDER == 7
+// relative error: 0x1.a72c2bf8p-58
+// abs error: 0x1.67a552c8p-66
+// in -0x1.f45p-8 0x1.f45p-8
+-0x1.71547652b8339p-1,
+0x1.ec709dc3a04bep-2,
+-0x1.7154764702ffbp-2,
+0x1.2776c50034c48p-2,
+-0x1.ec7b328ea92bcp-3,
+0x1.a6225e117f92ep-3,
+#endif
+},
+/* Algorithm:
+
+	x = 2^k z
+	log2(x) = k + log2(c) + log2(z/c)
+	log2(z/c) = poly(z/c - 1)
+
+where z is in [1.6p-1; 1.6p0] which is split into N subintervals and z falls
+into the ith one, then table entries are computed as
+
+	tab[i].invc = 1/c
+	tab[i].logc = (double)log2(c)
+	tab2[i].chi = (double)c
+	tab2[i].clo = (double)(c - (double)c)
+
+where c is near the center of the subinterval and is chosen by trying +-2^29
+floating point invc candidates around 1/center and selecting one for which
+
+	1) the rounding error in 0x1.8p10 + logc is 0,
+	2) the rounding error in z - chi - clo is < 0x1p-64 and
+	3) the rounding error in (double)log2(c) is minimized (< 0x1p-68).
+
+Note: 1) ensures that k + logc can be computed without rounding error, 2)
+ensures that z/c - 1 can be computed as (z - chi - clo)*invc with close to a
+single rounding error when there is no fast fma for z*invc - 1, 3) ensures
+that logc + poly(z/c - 1) has small error, however near x == 1 when
+|log2(x)| < 0x1p-4, this is not enough so that is special cased.  */
+.tab = {
+#if N == 64
+{0x1.724286bb1acf8p+0, -0x1.1095feecdb000p-1},
+{0x1.6e1f766d2cca1p+0, -0x1.08494bd76d000p-1},
+{0x1.6a13d0e30d48ap+0, -0x1.00143aee8f800p-1},
+{0x1.661ec32d06c85p+0, -0x1.efec5360b4000p-2},
+{0x1.623fa951198f8p+0, -0x1.dfdd91ab7e000p-2},
+{0x1.5e75ba4cf026cp+0, -0x1.cffae0cc79000p-2},
+{0x1.5ac055a214fb8p+0, -0x1.c043811fda000p-2},
+{0x1.571ed0f166e1ep+0, -0x1.b0b67323ae000p-2},
+{0x1.53909590bf835p+0, -0x1.a152f5a2db000p-2},
+{0x1.5014fed61adddp+0, -0x1.9217f5af86000p-2},
+{0x1.4cab88e487bd0p+0, -0x1.8304db0719000p-2},
+{0x1.49539b4334feep+0, -0x1.74189f9a9e000p-2},
+{0x1.460cbdfafd569p+0, -0x1.6552bb5199000p-2},
+{0x1.42d664ee4b953p+0, -0x1.56b23a29b1000p-2},
+{0x1.3fb01111dd8a6p+0, -0x1.483650f5fa000p-2},
+{0x1.3c995b70c5836p+0, -0x1.39de937f6a000p-2},
+{0x1.3991c4ab6fd4ap+0, -0x1.2baa1538d6000p-2},
+{0x1.3698e0ce099b5p+0, -0x1.1d98340ca4000p-2},
+{0x1.33ae48213e7b2p+0, -0x1.0fa853a40e000p-2},
+{0x1.30d191985bdb1p+0, -0x1.01d9c32e73000p-2},
+{0x1.2e025cab271d7p+0, -0x1.e857da2fa6000p-3},
+{0x1.2b404cf13cd82p+0, -0x1.cd3c8633d8000p-3},
+{0x1.288b02c7ccb50p+0, -0x1.b26034c14a000p-3},
+{0x1.25e2263944de5p+0, -0x1.97c1c2f4fe000p-3},
+{0x1.234563d8615b1p+0, -0x1.7d6023f800000p-3},
+{0x1.20b46e33eaf38p+0, -0x1.633a71a05e000p-3},
+{0x1.1e2eefdcda3ddp+0, -0x1.494f5e9570000p-3},
+{0x1.1bb4a580b3930p+0, -0x1.2f9e424e0a000p-3},
+{0x1.19453847f2200p+0, -0x1.162595afdc000p-3},
+{0x1.16e06c0d5d73cp+0, -0x1.f9c9a75bd8000p-4},
+{0x1.1485f47b7e4c2p+0, -0x1.c7b575bf9c000p-4},
+{0x1.12358ad0085d1p+0, -0x1.960c60ff48000p-4},
+{0x1.0fef00f532227p+0, -0x1.64ce247b60000p-4},
+{0x1.0db2077d03a8fp+0, -0x1.33f78b2014000p-4},
+{0x1.0b7e6d65980d9p+0, -0x1.0387d1a42c000p-4},
+{0x1.0953efe7b408dp+0, -0x1.a6f9208b50000p-5},
+{0x1.07325cac53b83p+0, -0x1.47a954f770000p-5},
+{0x1.05197e40d1b5cp+0, -0x1.d23a8c50c0000p-6},
+{0x1.03091c1208ea2p+0, -0x1.16a2629780000p-6},
+{0x1.0101025b37e21p+0, -0x1.720f8d8e80000p-8},
+{0x1.fc07ef9caa76bp-1, 0x1.6fe53b1500000p-7},
+{0x1.f4465d3f6f184p-1, 0x1.11ccce10f8000p-5},
+{0x1.ecc079f84107fp-1, 0x1.c4dfc8c8b8000p-5},
+{0x1.e573a99975ae8p-1, 0x1.3aa321e574000p-4},
+{0x1.de5d6f0bd3de6p-1, 0x1.918a0d08b8000p-4},
+{0x1.d77b681ff38b3p-1, 0x1.e72e9da044000p-4},
+{0x1.d0cb5724de943p-1, 0x1.1dcd2507f6000p-3},
+{0x1.ca4b2dc0e7563p-1, 0x1.476ab03dea000p-3},
+{0x1.c3f8ee8d6cb51p-1, 0x1.7074377e22000p-3},
+{0x1.bdd2b4f020c4cp-1, 0x1.98ede8ba94000p-3},
+{0x1.b7d6c006015cap-1, 0x1.c0db86ad2e000p-3},
+{0x1.b20366e2e338fp-1, 0x1.e840aafcee000p-3},
+{0x1.ac57026295039p-1, 0x1.0790ab4678000p-2},
+{0x1.a6d01bc2731ddp-1, 0x1.1ac056801c000p-2},
+{0x1.a16d3bc3ff18bp-1, 0x1.2db11d4fee000p-2},
+{0x1.9c2d14967feadp-1, 0x1.406464ec58000p-2},
+{0x1.970e4f47c9902p-1, 0x1.52dbe093af000p-2},
+{0x1.920fb3982bcf2p-1, 0x1.651902050d000p-2},
+{0x1.8d30187f759f1p-1, 0x1.771d2cdeaf000p-2},
+{0x1.886e5ebb9f66dp-1, 0x1.88e9c857d9000p-2},
+{0x1.83c97b658b994p-1, 0x1.9a80155e16000p-2},
+{0x1.7f405ffc61022p-1, 0x1.abe186ed3d000p-2},
+{0x1.7ad22181415cap-1, 0x1.bd0f2aea0e000p-2},
+{0x1.767dcf99eff8cp-1, 0x1.ce0a43dbf4000p-2},
+#endif
+},
+#ifndef __FP_FAST_FMA
+.tab2 = {
+# if N == 64
+{0x1.6200012b90a8ep-1, 0x1.904ab0644b605p-55},
+{0x1.66000045734a6p-1, 0x1.1ff9bea62f7a9p-57},
+{0x1.69fffc325f2c5p-1, 0x1.27ecfcb3c90bap-55},
+{0x1.6e00038b95a04p-1, 0x1.8ff8856739326p-55},
+{0x1.71fffe09994e3p-1, 0x1.afd40275f82b1p-55},
+{0x1.7600015590e1p-1, -0x1.2fd75b4238341p-56},
+{0x1.7a00012655bd5p-1, 0x1.808e67c242b76p-56},
+{0x1.7e0003259e9a6p-1, -0x1.208e426f622b7p-57},
+{0x1.81fffedb4b2d2p-1, -0x1.402461ea5c92fp-55},
+{0x1.860002dfafcc3p-1, 0x1.df7f4a2f29a1fp-57},
+{0x1.89ffff78c6b5p-1, -0x1.e0453094995fdp-55},
+{0x1.8e00039671566p-1, -0x1.a04f3bec77b45p-55},
+{0x1.91fffe2bf1745p-1, -0x1.7fa34400e203cp-56},
+{0x1.95fffcc5c9fd1p-1, -0x1.6ff8005a0695dp-56},
+{0x1.9a0003bba4767p-1, 0x1.0f8c4c4ec7e03p-56},
+{0x1.9dfffe7b92da5p-1, 0x1.e7fd9478c4602p-55},
+{0x1.a1fffd72efdafp-1, -0x1.a0c554dcdae7ep-57},
+{0x1.a5fffde04ff95p-1, 0x1.67da98ce9b26bp-55},
+{0x1.a9fffca5e8d2bp-1, -0x1.284c9b54c13dep-55},
+{0x1.adfffddad03eap-1, 0x1.812c8ea602e3cp-58},
+{0x1.b1ffff10d3d4dp-1, -0x1.efaddad27789cp-55},
+{0x1.b5fffce21165ap-1, 0x1.3cb1719c61237p-58},
+{0x1.b9fffd950e674p-1, 0x1.3f7d94194cep-56},
+{0x1.be000139ca8afp-1, 0x1.50ac4215d9bcp-56},
+{0x1.c20005b46df99p-1, 0x1.beea653e9c1c9p-57},
+{0x1.c600040b9f7aep-1, -0x1.c079f274a70d6p-56},
+{0x1.ca0006255fd8ap-1, -0x1.a0b4076e84c1fp-56},
+{0x1.cdfffd94c095dp-1, 0x1.8f933f99ab5d7p-55},
+{0x1.d1ffff975d6cfp-1, -0x1.82c08665fe1bep-58},
+{0x1.d5fffa2561c93p-1, -0x1.b04289bd295f3p-56},
+{0x1.d9fff9d228b0cp-1, 0x1.70251340fa236p-55},
+{0x1.de00065bc7e16p-1, -0x1.5011e16a4d80cp-56},
+{0x1.e200002f64791p-1, 0x1.9802f09ef62ep-55},
+{0x1.e600057d7a6d8p-1, -0x1.e0b75580cf7fap-56},
+{0x1.ea00027edc00cp-1, -0x1.c848309459811p-55},
+{0x1.ee0006cf5cb7cp-1, -0x1.f8027951576f4p-55},
+{0x1.f2000782b7dccp-1, -0x1.f81d97274538fp-55},
+{0x1.f6000260c450ap-1, -0x1.071002727ffdcp-59},
+{0x1.f9fffe88cd533p-1, -0x1.81bdce1fda8bp-58},
+{0x1.fdfffd50f8689p-1, 0x1.7f91acb918e6ep-55},
+{0x1.0200004292367p+0, 0x1.b7ff365324681p-54},
+{0x1.05fffe3e3d668p+0, 0x1.6fa08ddae957bp-55},
+{0x1.0a0000a85a757p+0, -0x1.7e2de80d3fb91p-58},
+{0x1.0e0001a5f3fccp+0, -0x1.1823305c5f014p-54},
+{0x1.11ffff8afbaf5p+0, -0x1.bfabb6680bac2p-55},
+{0x1.15fffe54d91adp+0, -0x1.d7f121737e7efp-54},
+{0x1.1a00011ac36e1p+0, 0x1.c000a0516f5ffp-54},
+{0x1.1e00019c84248p+0, -0x1.082fbe4da5dap-54},
+{0x1.220000ffe5e6ep+0, -0x1.8fdd04c9cfb43p-55},
+{0x1.26000269fd891p+0, 0x1.cfe2a7994d182p-55},
+{0x1.2a00029a6e6dap+0, -0x1.00273715e8bc5p-56},
+{0x1.2dfffe0293e39p+0, 0x1.b7c39dab2a6f9p-54},
+{0x1.31ffff7dcf082p+0, 0x1.df1336edc5254p-56},
+{0x1.35ffff05a8b6p+0, -0x1.e03564ccd31ebp-54},
+{0x1.3a0002e0eaeccp+0, 0x1.5f0e74bd3a477p-56},
+{0x1.3e000043bb236p+0, 0x1.c7dcb149d8833p-54},
+{0x1.4200002d187ffp+0, 0x1.e08afcf2d3d28p-56},
+{0x1.460000d387cb1p+0, 0x1.20837856599a6p-55},
+{0x1.4a00004569f89p+0, -0x1.9fa5c904fbcd2p-55},
+{0x1.4e000043543f3p+0, -0x1.81125ed175329p-56},
+{0x1.51fffcc027f0fp+0, 0x1.883d8847754dcp-54},
+{0x1.55ffffd87b36fp+0, -0x1.709e731d02807p-55},
+{0x1.59ffff21df7bap+0, 0x1.7f79f68727b02p-55},
+{0x1.5dfffebfc3481p+0, -0x1.180902e30e93ep-54},
+# endif
+},
+#endif /* __FP_FAST_FMA */
+};
diff --git a/sysdeps/ieee754/dbl-64/math_config.h b/sysdeps/ieee754/dbl-64/math_config.h
index 2eb793d4c8..9c3ea1d436 100644
--- a/sysdeps/ieee754/dbl-64/math_config.h
+++ b/sysdeps/ieee754/dbl-64/math_config.h
@@ -149,4 +149,20 @@ extern const struct log_data
 #endif
 } __log_data attribute_hidden;
 
+#define LOG2_TABLE_BITS 6
+#define LOG2_POLY_ORDER 7
+#define LOG2_POLY1_ORDER 11
+extern const struct log2_data
+{
+  double invln2hi;
+  double invln2lo;
+  double poly[LOG2_POLY_ORDER - 1];
+  double poly1[LOG2_POLY1_ORDER - 1];
+  /* See e_log2_data.c for details.  */
+  struct {double invc, logc;} tab[1 << LOG2_TABLE_BITS];
+#ifndef __FP_FAST_FMA
+  struct {double chi, clo;} tab2[1 << LOG2_TABLE_BITS];
+#endif
+} __log2_data attribute_hidden;
+
 #endif
diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/e_log2.c b/sysdeps/ieee754/dbl-64/wordsize-64/e_log2.c
deleted file mode 100644
index f08d5b337d..0000000000
--- a/sysdeps/ieee754/dbl-64/wordsize-64/e_log2.c
+++ /dev/null
@@ -1,128 +0,0 @@
-/*
- * ====================================================
- * 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.
- * ====================================================
- */
-
-/* __ieee754_log2(x)
- * Return the logarithm to base 2 of x
- *
- * Method :
- *   1. Argument Reduction: find k and f such that
- *			x = 2^k * (1+f),
- *	   where  sqrt(2)/2 < 1+f < sqrt(2) .
- *
- *   2. Approximation of log(1+f).
- *	Let s = f/(2+f) ; based on log(1+f) = log(1+s) - log(1-s)
- *		 = 2s + 2/3 s**3 + 2/5 s**5 + .....,
- *		 = 2s + s*R
- *      We use a special Reme algorithm on [0,0.1716] to generate
- *	a polynomial of degree 14 to approximate R The maximum error
- *	of this polynomial approximation is bounded by 2**-58.45. In
- *	other words,
- *			2      4      6      8      10      12      14
- *	    R(z) ~ Lg1*s +Lg2*s +Lg3*s +Lg4*s +Lg5*s  +Lg6*s  +Lg7*s
- *	(the values of Lg1 to Lg7 are listed in the program)
- *	and
- *	    |      2          14          |     -58.45
- *	    | Lg1*s +...+Lg7*s    -  R(z) | <= 2
- *	    |                             |
- *	Note that 2s = f - s*f = f - hfsq + s*hfsq, where hfsq = f*f/2.
- *	In order to guarantee error in log below 1ulp, we compute log
- *	by
- *		log(1+f) = f - s*(f - R)	(if f is not too large)
- *		log(1+f) = f - (hfsq - s*(hfsq+R)).	(better accuracy)
- *
- *	3. Finally,  log(x) = k + log(1+f).
- *			    = k+(f-(hfsq-(s*(hfsq+R))))
- *
- * Special cases:
- *	log2(x) is NaN with signal if x < 0 (including -INF) ;
- *	log2(+INF) is +INF; log(0) is -INF with signal;
- *	log2(NaN) is that NaN with no signal.
- *
- * Constants:
- * The hexadecimal values are the intended ones for the following
- * constants. The decimal values may be used, provided that the
- * compiler will convert from decimal to binary accurately enough
- * to produce the hexadecimal values shown.
- */
-
-#include <math.h>
-#include <math_private.h>
-
-static const double ln2 = 0.69314718055994530942;
-static const double two54 = 1.80143985094819840000e+16;	/* 4350000000000000 */
-static const double Lg1 = 6.666666666666735130e-01;	/* 3FE5555555555593 */
-static const double Lg2 = 3.999999999940941908e-01;	/* 3FD999999997FA04 */
-static const double Lg3 = 2.857142874366239149e-01;	/* 3FD2492494229359 */
-static const double Lg4 = 2.222219843214978396e-01;	/* 3FCC71C51D8E78AF */
-static const double Lg5 = 1.818357216161805012e-01;	/* 3FC7466496CB03DE */
-static const double Lg6 = 1.531383769920937332e-01;	/* 3FC39A09D078C69F */
-static const double Lg7 = 1.479819860511658591e-01;	/* 3FC2F112DF3E5244 */
-
-static const double zero = 0.0;
-
-double
-__ieee754_log2 (double x)
-{
-  double hfsq, f, s, z, R, w, t1, t2, dk;
-  int64_t hx, i, j;
-  int32_t k;
-
-  EXTRACT_WORDS64 (hx, x);
-
-  k = 0;
-  if (hx < INT64_C(0x0010000000000000))
-    {				/* x < 2**-1022  */
-      if (__glibc_unlikely ((hx & UINT64_C(0x7fffffffffffffff)) == 0))
-	return -two54 / fabs (x);	/* log(+-0)=-inf */
-      if (__glibc_unlikely (hx < 0))
-	return (x - x) / (x - x);	/* log(-#) = NaN */
-      k -= 54;
-      x *= two54;		/* subnormal number, scale up x */
-      EXTRACT_WORDS64 (hx, x);
-    }
-  if (__glibc_unlikely (hx >= UINT64_C(0x7ff0000000000000)))
-    return x + x;
-  k += (hx >> 52) - 1023;
-  hx &= UINT64_C(0x000fffffffffffff);
-  i = (hx + UINT64_C(0x95f6400000000)) & UINT64_C(0x10000000000000);
-  /* normalize x or x/2 */
-  INSERT_WORDS64 (x, hx | (i ^ UINT64_C(0x3ff0000000000000)));
-  k += (i >> 52);
-  dk = (double) k;
-  f = x - 1.0;
-  if ((UINT64_C(0x000fffffffffffff) & (2 + hx)) < 3)
-    {				/* |f| < 2**-20 */
-      if (f == zero)
-	return dk;
-      R = f * f * (0.5 - 0.33333333333333333 * f);
-      return dk - (R - f) / ln2;
-    }
-  s = f / (2.0 + f);
-  z = s * s;
-  i = hx - UINT64_C(0x6147a00000000);
-  w = z * z;
-  j = UINT64_C(0x6b85100000000) - hx;
-  t1 = w * (Lg2 + w * (Lg4 + w * Lg6));
-  t2 = z * (Lg1 + w * (Lg3 + w * (Lg5 + w * Lg7)));
-  i |= j;
-  R = t2 + t1;
-  if (i > 0)
-    {
-      hfsq = 0.5 * f * f;
-      return dk - ((hfsq - (s * (hfsq + R))) - f) / ln2;
-    }
-  else
-    {
-      return dk - ((s * (f - R)) - f) / ln2;
-    }
-}
-
-strong_alias (__ieee754_log2, __log2_finite)
diff --git a/sysdeps/m68k/m680x0/fpu/e_log2_data.c b/sysdeps/m68k/m680x0/fpu/e_log2_data.c
new file mode 100644
index 0000000000..1cc8931700
--- /dev/null
+++ b/sysdeps/m68k/m680x0/fpu/e_log2_data.c
@@ -0,0 +1 @@
+/* Not needed.  */