log1p: Provide replacement for Minix and MSVC.

* lib/math.in.h (log1p): New declaration.
* lib/log1p.c: New file.
* m4/log1p.m4: New file.
* m4/math_h.m4 (gl_MATH_H): Test whether log1p is declared.
(gl_MATH_H_DEFAULTS): Initialize GNULIB_LOG1P, HAVE_LOG1P.
* modules/math (Makefile.am): Substitute GNULIB_LOG1P, HAVE_LOG1P.
* modules/log1p (Files): Add lib/log1p.c, m4/log1p.m4.
(Depends-on): Add math, isnand, log, round.
(configure.ac): Invoke gl_FUNC_LOG1P. Arrange to compile replacement if
HAVE_LOG1P is 0.
* tests/test-math-c++.cc: Check the declaration of log1p.
* doc/posix-functions/log1p.texi: Mention the replacement.

9 files changed, 617 insertions, 7 deletions

diff --git a/ChangeLog b/ChangeLog
index 2deb869ea4..ba7e6950f7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,21 @@
 2012-03-10  Bruno Haible  <bruno@clisp.org>
 
+	log1p: Provide replacement for Minix and MSVC.
+	* lib/math.in.h (log1p): New declaration.
+	* lib/log1p.c: New file.
+	* m4/log1p.m4: New file.
+	* m4/math_h.m4 (gl_MATH_H): Test whether log1p is declared.
+	(gl_MATH_H_DEFAULTS): Initialize GNULIB_LOG1P, HAVE_LOG1P.
+	* modules/math (Makefile.am): Substitute GNULIB_LOG1P, HAVE_LOG1P.
+	* modules/log1p (Files): Add lib/log1p.c, m4/log1p.m4.
+	(Depends-on): Add math, isnand, log, round.
+	(configure.ac): Invoke gl_FUNC_LOG1P. Arrange to compile replacement if
+	HAVE_LOG1P is 0.
+	* tests/test-math-c++.cc: Check the declaration of log1p.
+	* doc/posix-functions/log1p.texi: Mention the replacement.
+
+2012-03-10  Bruno Haible  <bruno@clisp.org>
+
 	math tests: Small simplification.
 	* tests/test-exp.h (test_function): Use the same err_bound for
 	'double' on platforms with sizeof (long double) == sizeof (double)
diff --git a/doc/posix-functions/log1p.texi b/doc/posix-functions/log1p.texi
index d8f83fcd2c..a63b75b194 100644
--- a/doc/posix-functions/log1p.texi
+++ b/doc/posix-functions/log1p.texi
@@ -8,11 +8,11 @@ Gnulib module: log1p
 
 Portability problems fixed by Gnulib:
 @itemize
+@item
+This function is missing on some platforms:
+Minix 3.1.8, MSVC 9.
 @end itemize
 
 Portability problems not fixed by Gnulib:
 @itemize
-@item
-This function is missing on some platforms:
-Minix 3.1.8, MSVC 9.
 @end itemize
diff --git a/lib/log1p.c b/lib/log1p.c
new file mode 100644
index 0000000000..c50f89fc54
--- /dev/null
+++ b/lib/log1p.c
@@ -0,0 +1,518 @@
+/* Natural logarithm of 1 plus argument.
+   Copyright (C) 2012 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <math.h>
+
+double
+log1p (double x)
+{
+  if (isnand (x))
+    return x;
+
+  if (x <= -1.0)
+    {
+      if (x == -1.0)
+        /* Return -Infinity.  */
+        return - HUGE_VAL;
+      else
+        {
+          /* Return NaN.  */
+#if defined _MSC_VER || (defined __sgi && !defined __GNUC__)
+          static double zero;
+          return zero / zero;
+#else
+          return 0.0 / 0.0;
+#endif
+        }
+    }
+
+  if (x < -0.5 || x > 1.0)
+    return log (1.0 + x);
+  /* Here -0.5 <= x <= 1.0.  */
+
+  if (x == 0.0)
+    /* Return a zero with the same sign as x.  */
+    return x;
+
+  /* Decompose x into
+       1 + x = (1 + m/256) * (1 + y)
+     where
+       m is an integer, -128 <= m <= 256,
+       y is a number, |y| <= 1/256.
+     y is computed as
+       y = (256 * x - m) / (256 + m).
+     Then
+       log(1+x) = log(m/256) + log(1+y)
+     The first summand is a table lookup.
+     The second summand is computed
+       - either through the power series
+           log(1+y) = y
+                      - 1/2 * y^2
+                      + 1/3 * y^3
+                      - 1/4 * y^4
+                      + 1/5 * y^5
+                      - 1/6 * y^6
+                      + 1/7 * y^7
+                      - 1/8 * y^8
+                      + 1/9 * y^9
+                      - 1/10 * y^10
+                      + 1/11 * y^11
+                      - 1/12 * y^12
+                      + 1/13 * y^13
+                      - 1/14 * y^14
+                      + 1/15 * y^15
+                      - ...
+       - or as log(1+y) = log((1+z)/(1-z)) = 2 * atanh(z)
+         where z = y/(2+y)
+         and atanh(z) is computed through its power series:
+           atanh(z) = z
+                      + 1/3 * z^3
+                      + 1/5 * z^5
+                      + 1/7 * z^7
+                      + 1/9 * z^9
+                      + 1/11 * z^11
+                      + 1/13 * z^13
+                      + 1/15 * z^15
+                      + ...
+         Since |z| <= 1/511 < 0.002, the relative contribution of the z^9
+         term is < 1/9*0.002^8 < 2^-60 <= 2^-DBL_MANT_DIG, therefore we
+         can truncate the series after the z^7 term.  */
+
+  {
+    double m = round (x * 256.0);
+    double y = ((x * 256.0) - m) / (m + 256.0);
+    double z = y / (2.0 + y);
+
+/* Coefficients of the power series for atanh(z).  */
+#define ATANH_COEFF_1  1.0
+#define ATANH_COEFF_3  0.333333333333333333333333333333333333334
+#define ATANH_COEFF_5  0.2
+#define ATANH_COEFF_7  0.142857142857142857142857142857142857143
+#define ATANH_COEFF_9  0.1111111111111111111111111111111111111113
+#define ATANH_COEFF_11 0.090909090909090909090909090909090909091
+#define ATANH_COEFF_13 0.076923076923076923076923076923076923077
+#define ATANH_COEFF_15 0.066666666666666666666666666666666666667
+
+    double z2 = z * z;
+    double atanh_z =
+      (((ATANH_COEFF_7
+         * z2 + ATANH_COEFF_5)
+        * z2 + ATANH_COEFF_3)
+       * z2 + ATANH_COEFF_1)
+      * z;
+
+    /* log_table[i] = log((i + 128) / 256).
+       Computed in GNU clisp through
+         (setf (long-float-digits) 128)
+         (setq a 0L0)
+         (setf (long-float-digits) 256)
+         (dotimes (i 385)
+           (format t "        ~D,~%"
+                   (float (log (* (/ (+ i 128) 256) 1L0)) a)))  */
+    static const double log_table[385] =
+      {
+        -0.693147180559945309417232121458176568075,
+        -0.6853650401178903604697692213970398044,
+        -0.677642994023980055266378075415729732197,
+        -0.669980121278410931188432960495886651496,
+        -0.662375521893191621046203913861404403985,
+        -0.65482831625780871022347679633437927773,
+        -0.647337644528651106250552853843513225963,
+        -0.639902666041133026551361927671647791137,
+        -0.632522558743510466836625989417756304788,
+        -0.625196518651437560022666843685547154042,
+        -0.617923759322357783718626781474514153438,
+        -0.61070351134887071814907205278986876216,
+        -0.60353502187025817679728065207969203929,
+        -0.59641755410139419712166106497071313106,
+        -0.58935038687830174459117031769420187977,
+        -0.582332814219655195222425952134964639978,
+        -0.575364144903561854878438011987654863008,
+        -0.568443702058988073553825606077313299585,
+        -0.561570822771226036828515992768693405624,
+        -0.554744857700826173731906247856527380683,
+        -0.547965170715447412135297057717612244552,
+        -0.541231138534103334345428696561292056747,
+        -0.534542150383306725323860946832334992828,
+        -0.527897607664638146541620672180936254347,
+        -0.52129692363328608707713317540302930314,
+        -0.514739523087127012297831879947234599722,
+        -0.50822484206593331675332852879892694707,
+        -0.50175232756031585480793331389686769463,
+        -0.495321437230025429054660050261215099,
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+        0.318453731118534615810247213590599595595,
+        0.321290612453734292057863145522557457887,
+        0.324119468654211976090670760434987352183,
+        0.326940344995853320592356894073809191681,
+        0.329753286372467981814422811920789810952,
+        0.332558337300076601412275626573419425269,
+        0.335355541921137830257179579814166199074,
+        0.338144944008716397710235913939267433111,
+        0.340926586970593210305089199780356208443,
+        0.34370051385331844468019789211029452987,
+        0.346466767346208580918462188425772950712,
+        0.349225389785288304181275421187371759687,
+        0.35197642315717818465544745625943892599,
+        0.354719909102929028355011218999317665826,
+        0.357455888921803774226009490140904474434,
+        0.360184403575007796281574967493016620926,
+        0.362905493689368453137824345977489846141,
+        0.365619199560964711319396875217046453067,
+        0.368325561158707653048230154050398826898,
+        0.371024618127872663911964910806824955394,
+        0.373716409793584080821016832715823506644,
+        0.376400975164253065997877633436251593315,
+        0.379078352934969458390853345631019858882,
+        0.38174858149084833985966626493567607862,
+        0.384411698910332039734790062481290868519,
+        0.387067742968448287898902502261817665695,
+        0.38971675114002521337046360400352086705,
+        0.392358760602863872479379611988215363485,
+        0.39499380824086897810639403636498176831,
+        0.397621930647138489104829072973405554918,
+        0.40024316412701270692932510199513117008,
+        0.402857544701083514655197565487057707577,
+        0.405465108108164381978013115464349136572,
+        0.408065889808221748430198682969084124381,
+        0.410659924985268385934306203175822787661,
+        0.41324724855021933092547601552548590025,
+        0.415827895143710965613328892954902305356,
+        0.418401899138883817510763261966760106515,
+        0.42096929464412963612886716150679597245,
+        0.423530115505803295718430478017910109426,
+        0.426084395310900063124544879595476618897,
+        0.428632167389698760206812276426639053152,
+        0.43117346481837134085917247895559499848,
+        0.433708320421559393435847903042186017095,
+        0.436236766774918070349041323061121300663,
+        0.438758836207627937745575058511446738878,
+        0.441274560804875229489496441661301225362,
+        0.443783972410300981171768440588146426918,
+        0.446287102628419511532590180619669006749,
+        0.448783982827006710512822115683937186274,
+        0.451274644139458585144692383079012478686,
+        0.453759117467120506644794794442263270651,
+        0.456237433481587594380805538163929748437,
+        0.458709622626976664843883309250877913511,
+        0.461175715122170166367999925597855358603,
+        0.463635740963032513092182277331163919118,
+        0.466089729924599224558619247504769399859,
+        0.468537711563239270375665237462973542708,
+        0.470979715218791012546897856056359251373,
+        0.473415770016672131372578393236978550606,
+        0.475845904869963914265209586304381412175,
+        0.478270148481470280383546145497464809096,
+        0.480688529345751907676618455448011551209,
+        0.48310107575113582273837458485214554795,
+        0.485507815781700807801791077190788900579,
+        0.487908777319238973246173184132656942487,
+        0.490303988045193838150346159645746860531,
+        0.492693475442575255695076950020077845328,
+        0.495077266797851514597964584842833665358,
+        0.497455389202818942250859256731684928918,
+        0.499827869556449329821331415247044141512,
+        0.502194734566715494273584171951812573586,
+        0.504556010752395287058308531738174929982,
+        0.506911724444854354113196312660089270034,
+        0.509261901789807946804074919228323824878,
+        0.51160656874906207851888487520338193135,
+        0.51394575110223431680100608827421759311,
+        0.51627947444845449617281928478756106467,
+        0.518607764208045632152976996364798698556,
+        0.520930645624185312409809834659637709188,
+        0.52324814376454783651680722493487084164,
+        0.525560283522927371382427602307131424923,
+        0.527867089620842385113892217778300963557,
+        0.530168586609121617841419630845212405063,
+        0.532464798869471843873923723460142242606,
+        0.534755750616027675477923292032637111077,
+        0.537041465896883654566729244153832299024,
+        0.539321968595608874655355158077341155752,
+        0.54159728243274437157654230390043409897,
+        0.543867430967283517663338989065998323965,
+        0.546132437598135650382397209231209163864,
+        0.548392325565573162748150286179863158565,
+        0.550647117952662279259948179204913460093,
+        0.552896837686677737580717902230624314327,
+        0.55514150754050159271548035951590405017,
+        0.557381150134006357049816540361233647898,
+        0.559615787935422686270888500526826593487,
+        0.561845443262691817915664819160697456814,
+        0.564070138284802966071384290090190711817,
+        0.566289895023115872590849979337124343595,
+        0.568504735352668712078738764866962263577,
+        0.5707146810034715448536245647415894503,
+        0.572919753561785509092756726626261068625,
+        0.575119974471387940421742546569273429365,
+        0.577315365034823604318112061519496401506,
+        0.579505946414642223855274409488070989814,
+        0.58169173963462248252061075372537234071,
+        0.583872765580982679097413356975291104927,
+        0.586049045003578208904119436287324349516,
+        0.588220598517086043034868221609113995052,
+        0.590387446602176374641916708123598757576,
+        0.59254960960667159874199020959329739696,
+        0.594707107746692789514343546529205333192,
+        0.59685996110779383658731192302565801002,
+        0.59900818964608339938160002446165150206,
+        0.601151813189334836191674317068856441547,
+        0.603290851438084262340585186661310605647,
+        0.6054253239667168894375677681414899356,
+        0.607555250224541795501085152791125371894,
+        0.609680649536855273481833501660588408785,
+        0.611801541105992903529889766428814783686,
+        0.613917944012370492196929119645563790777,
+        0.616029877215514019647565928196700650293,
+        0.618137359555078733872689126674816271683,
+        0.620240409751857528851494632567246856773,
+        0.62233904640877874159710264120869663505,
+        0.62443328801189350104253874405467311991,
+        0.626523152931352759778820859734204069282,
+        0.628608659422374137744308205774183639946,
+        0.6306898256261987050837261409313532241,
+        0.63276666957103782954578646850357975849,
+        0.634839209173010211969493840510489008123,
+        0.63690746223706923162049442718119919119,
+        0.63897144645792072137962398326473680873,
+        0.64103117942093129105560133440539254671,
+        0.643086678603027315392053859585132960477,
+        0.645137961373584701665228496134731905937,
+        0.647185044995309550122320631377863036675,
+        0.64922794662510981889083996990531112227,
+        0.651266683314958103396333353349672108398,
+        0.653301272012745638758615881210873884572,
+        0.65533172956312763209494967856962559648,
+        0.657358072708360030141890023245936165513,
+        0.659380318089127826115336413370955804038,
+        0.661398482245365008260235838709650938148,
+        0.66341258161706625109695030429080128179,
+        0.665422632545090448950092610006660181147,
+        0.667428651271956189947234166318980478403,
+        0.669430653942629267298885270929503510123,
+        0.67142865660530232331713904200189252584,
+        0.67342267521216672029796038880101726475,
+        0.67541272562017673108090414397019748722,
+        0.677398823591806140809682609997348298556,
+        0.67938098479579735014710062847376425181,
+        0.681359224807903068948071559568089441735,
+        0.683333559111620688164363148387750369654,
+        0.68530400309891941654404807896723298642,
+        0.687270572070960267497006884394346103924,
+        0.689233281238808980324914337814603903233,
+        0.691192145724141958859604629216309755938,
+        0.693147180559945309417232121458176568075
+      };
+    return log_table[128 + (int)m] + 2.0 * atanh_z;
+  }
+}
diff --git a/lib/math.in.h b/lib/math.in.h
index 2e1d322598..a479b6d31d 100644
--- a/lib/math.in.h
+++ b/lib/math.in.h
@@ -1221,6 +1221,21 @@ _GL_WARN_ON_USE (log10l, "log10l is unportable - "
 #endif
 
 
+#if @GNULIB_LOG1P@
+# if !@HAVE_LOG1P@
+_GL_FUNCDECL_SYS (log1p, double, (double x));
+# endif
+_GL_CXXALIAS_SYS (log1p, double, (double x));
+_GL_CXXALIASWARN (log1p);
+#elif defined GNULIB_POSIXCHECK
+# undef log1p
+# if HAVE_RAW_DECL_LOG1P
+_GL_WARN_ON_USE (log1p, "log1p has portability problems - "
+                 "use gnulib module log1p for portability");
+# endif
+#endif
+
+
 #if @GNULIB_MODFF@
 # if @REPLACE_MODFF@
 #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
diff --git a/m4/log1p.m4 b/m4/log1p.m4
new file mode 100644
index 0000000000..f692ca023e
--- /dev/null
+++ b/m4/log1p.m4
@@ -0,0 +1,45 @@
+# log1p.m4 serial 1
+dnl Copyright (C) 2012 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_LOG1P],
+[
+  AC_REQUIRE([gl_MATH_H_DEFAULTS])
+
+  dnl Persuade glibc <math.h> to declare log1p().
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
+  dnl Determine LOG1P_LIBM.
+  gl_COMMON_DOUBLE_MATHFUNC([log1p])
+
+  dnl Test whether log1p() exists.
+  save_LIBS="$LIBS"
+  LIBS="$LIBS $LOG1P_LIBM"
+  AC_CHECK_FUNCS([log1p])
+  LIBS="$save_LIBS"
+  if test $ac_cv_func_log1p = no; then
+    HAVE_LOG1P=0
+    dnl Find libraries needed to link lib/log1p.c.
+    AC_REQUIRE([gl_FUNC_ISNAND])
+    AC_REQUIRE([gl_FUNC_LOG])
+    AC_REQUIRE([gl_FUNC_ROUND])
+    LOG1P_LIBM=
+    dnl Append $ISNAND_LIBM to LOG1P_LIBM, avoiding gratuitous duplicates.
+    case " $LOG1P_LIBM " in
+      *" $ISNAND_LIBM "*) ;;
+      *) LOG1P_LIBM="$LOG1P_LIBM $ISNAND_LIBM" ;;
+    esac
+    dnl Append $LOG_LIBM to LOG1P_LIBM, avoiding gratuitous duplicates.
+    case " $LOG1P_LIBM " in
+      *" $LOG_LIBM "*) ;;
+      *) LOG1P_LIBM="$LOG1P_LIBM $LOG_LIBM" ;;
+    esac
+    dnl Append $ROUND_LIBM to LOG1P_LIBM, avoiding gratuitous duplicates.
+    case " $LOG1P_LIBM " in
+      *" $ROUND_LIBM "*) ;;
+      *) LOG1P_LIBM="$LOG1P_LIBM $ROUND_LIBM" ;;
+    esac
+  fi
+])
diff --git a/m4/math_h.m4 b/m4/math_h.m4
index 7b93ad9706..028d8cd1bb 100644
--- a/m4/math_h.m4
+++ b/m4/math_h.m4
@@ -1,4 +1,4 @@
-# math_h.m4 serial 95
+# math_h.m4 serial 96
 dnl Copyright (C) 2007-2012 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -44,7 +44,7 @@ AC_DEFUN([gl_MATH_H],
      expf expl exp2 exp2f exp2l expm1 expm1f expm1l
      fabsf fabsl floorf floorl fma fmaf fmal
      fmod fmodf fmodl frexpf frexpl hypotf hypotl
-     ldexpf ldexpl logb log logf logl log10f log10l modf modff modfl powf
+     ldexpf ldexpl logb log logf logl log10f log10l log1p modf modff modfl powf
      remainder remainderf remainderl
      rint rintf rintl round roundf roundl sinf sinl sinhf sqrtf sqrtl
      tanf tanl tanhf trunc truncf truncl])
@@ -119,6 +119,7 @@ AC_DEFUN([gl_MATH_H_DEFAULTS],
   GNULIB_LOGL=0;       AC_SUBST([GNULIB_LOGL])
   GNULIB_LOG10F=0;     AC_SUBST([GNULIB_LOG10F])
   GNULIB_LOG10L=0;     AC_SUBST([GNULIB_LOG10L])
+  GNULIB_LOG1P=0;      AC_SUBST([GNULIB_LOG1P])
   GNULIB_MODF=0;       AC_SUBST([GNULIB_MODF])
   GNULIB_MODFF=0;      AC_SUBST([GNULIB_MODFF])
   GNULIB_MODFL=0;      AC_SUBST([GNULIB_MODFL])
@@ -182,6 +183,7 @@ AC_DEFUN([gl_MATH_H_DEFAULTS],
   HAVE_LOGL=1;                 AC_SUBST([HAVE_LOGL])
   HAVE_LOG10F=1;               AC_SUBST([HAVE_LOG10F])
   HAVE_LOG10L=1;               AC_SUBST([HAVE_LOG10L])
+  HAVE_LOG1P=1;                AC_SUBST([HAVE_LOG1P])
   HAVE_MODFF=1;                AC_SUBST([HAVE_MODFF])
   HAVE_MODFL=1;                AC_SUBST([HAVE_MODFL])
   HAVE_POWF=1;                 AC_SUBST([HAVE_POWF])
diff --git a/modules/log1p b/modules/log1p
index 3470e87302..e055026aac 100644
--- a/modules/log1p
+++ b/modules/log1p
@@ -2,13 +2,23 @@ Description:
 log1p() function: natural logarithm of 1 plus argument.
 
 Files:
+lib/log1p.c
+m4/log1p.m4
 m4/mathfunc.m4
 
 Depends-on:
+math
 extensions
+isnand          [test $HAVE_LOG1P = 0]
+log             [test $HAVE_LOG1P = 0]
+round           [test $HAVE_LOG1P = 0]
 
 configure.ac:
-gl_COMMON_DOUBLE_MATHFUNC([log1p])
+gl_FUNC_LOG1P
+if test $HAVE_LOG1P = 0; then
+  AC_LIBOBJ([log1p])
+fi
+gl_MATH_MODULE_INDICATOR([log1p])
 
 Makefile.am:
 
diff --git a/modules/math b/modules/math
index 705e0b07eb..6c46eb0c21 100644
--- a/modules/math
+++ b/modules/math
@@ -86,6 +86,7 @@ math.h: math.in.h $(top_builddir)/config.status $(CXXDEFS_H) $(ARG_NONNULL_H) $(
 	      -e 's/@''GNULIB_LOGL''@/$(GNULIB_LOGL)/g' \
 	      -e 's/@''GNULIB_LOG10F''@/$(GNULIB_LOG10F)/g' \
 	      -e 's/@''GNULIB_LOG10L''@/$(GNULIB_LOG10L)/g' \
+	      -e 's/@''GNULIB_LOG1P''@/$(GNULIB_LOG1P)/g' \
 	      -e 's/@''GNULIB_MODF''@/$(GNULIB_MODF)/g' \
 	      -e 's/@''GNULIB_MODFF''@/$(GNULIB_MODFF)/g' \
 	      -e 's/@''GNULIB_MODFL''@/$(GNULIB_MODFL)/g' \
@@ -149,6 +150,7 @@ math.h: math.in.h $(top_builddir)/config.status $(CXXDEFS_H) $(ARG_NONNULL_H) $(
 	      -e 's|@''HAVE_LOGL''@|$(HAVE_LOGL)|g' \
 	      -e 's|@''HAVE_LOG10F''@|$(HAVE_LOG10F)|g' \
 	      -e 's|@''HAVE_LOG10L''@|$(HAVE_LOG10L)|g' \
+	      -e 's|@''HAVE_LOG1P''@|$(HAVE_LOG1P)|g' \
 	      -e 's|@''HAVE_MODFF''@|$(HAVE_MODFF)|g' \
 	      -e 's|@''HAVE_MODFL''@|$(HAVE_MODFL)|g' \
 	      -e 's|@''HAVE_POWF''@|$(HAVE_POWF)|g' \
diff --git a/tests/test-math-c++.cc b/tests/test-math-c++.cc
index a5619b29a7..3b25714f4c 100644
--- a/tests/test-math-c++.cc
+++ b/tests/test-math-c++.cc
@@ -215,7 +215,9 @@ SIGNATURE_CHECK (GNULIB_NAMESPACE::ldexpl, long double, (long double, int));
 SIGNATURE_CHECK (GNULIB_NAMESPACE::log10l, long double, (long double));
 #endif
 
-//SIGNATURE_CHECK (GNULIB_NAMESPACE::log1p, double, (double));
+#if GNULIB_TEST_LOG1P
+SIGNATURE_CHECK (GNULIB_NAMESPACE::log1p, double, (double));
+#endif
 
 //SIGNATURE_CHECK (GNULIB_NAMESPACE::logb, double, (double));