--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2007-02-25  Bruno Haible  <bruno@clisp.org>
+
+	* modules/printf-frexp: New file.
+	* lib/printf-frexp.h: New file.
+	* lib/printf-frexp.c: New file.
+	* m4/printf-frexp.m4: New file.
+
 2007-02-25  Bruno Haible  <bruno@clisp.org>
 
 	Assume automake >= 1.10 for the tests.

new file mode 100644
--- /dev/null
+++ b/lib/printf-frexp.c
@@ -0,0 +1,183 @@
+/* Split a double into fraction and mantissa, for hexadecimal printf.
+   Copyright (C) 2007 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 2, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#include <config.h>
+
+#if !(defined USE_LONG_DOUBLE && !HAVE_LONG_DOUBLE)
+
+/* Specification.  */
+# ifdef USE_LONG_DOUBLE
+#  include "printf-frexpl.h"
+# else
+#  include "printf-frexp.h"
+# endif
+
+# include <float.h>
+# include <math.h>
+# include "verify.h"
+
+/* This file assumes FLT_RADIX is 2.  */
+verify (FLT_RADIX == 2);
+
+# ifdef USE_LONG_DOUBLE
+#  define FUNC printf_frexpl
+#  define DOUBLE long double
+#  define MIN_EXP LDBL_MIN_EXP
+#  if HAVE_FREXPL_IN_LIBC && HAVE_LDEXPL_IN_LIBC
+#   define USE_FREXP_LDEXP
+#   define FREXP frexpl
+#   define LDEXP ldexpl
+#  endif
+#  define L_(literal) literal##L
+# else
+#  define FUNC printf_frexp
+#  define DOUBLE double
+#  define MIN_EXP DBL_MIN_EXP
+#  if HAVE_FREXP_IN_LIBC && HAVE_LDEXP_IN_LIBC
+#   define USE_FREXP_LDEXP
+#   define FREXP frexp
+#   define LDEXP ldexp
+#  endif
+#  define L_(literal) literal
+# endif
+
+DOUBLE
+FUNC (DOUBLE x, int *exp)
+{
+  int exponent;
+
+# ifdef USE_FREXP_LDEXP
+  /* frexp and ldexp are usually faster than the loop below.  */
+  x = FREXP (x, &exponent);
+
+  x = x + x;
+  exponent -= 1;
+
+  if (exponent < MIN_EXP - 1)
+    {
+      x = LDEXP (x, exponent - (MIN_EXP - 1));
+      exponent = MIN_EXP - 1;
+    }
+# else
+  /* Since the exponent is an 'int', it fits in 64 bits.  Therefore the
+     loops are executed no more than 64 times.  */
+  DOUBLE pow2[64]; /* pow2[i] = 2^2^i */
+  DOUBLE powh[64]; /* powh[i] = 2^-2^i */
+  int i;
+
+  exponent = 0;
+  if (x >= L_(1.0))
+    {
+      /* A nonnegative exponent.  */
+      {
+	DOUBLE pow2_i; /* = pow2[i] */
+	DOUBLE powh_i; /* = powh[i] */
+
+	/* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
+	   x * 2^exponent = argument, x >= 1.0.  */
+	for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
+	     ;
+	     i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
+	  {
+	    if (x >= pow2_i)
+	      {
+		exponent += (1 << i);
+		x *= powh_i;
+	      }
+	    else
+	      break;
+
+	    pow2[i] = pow2_i;
+	    powh[i] = powh_i;
+	  }
+      }
+      /* Here 1.0 <= x < 2^2^i.  */
+    }
+  else
+    {
+      /* A negative exponent.  */
+      {
+	DOUBLE pow2_i; /* = pow2[i] */
+	DOUBLE powh_i; /* = powh[i] */
+
+	/* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
+	   x * 2^exponent = argument, x < 1.0, exponent >= MIN_EXP - 1.  */
+	for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
+	     ;
+	     i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
+	  {
+	    if (exponent - (1 << i) < MIN_EXP - 1)
+	      break;
+
+	    exponent -= (1 << i);
+	    x *= pow2_i;
+	    if (x >= L_(1.0))
+	      break;
+
+	    pow2[i] = pow2_i;
+	    powh[i] = powh_i;
+	  }
+      }
+      /* Here either x < 1.0 and exponent - 2^i < MIN_EXP - 1 <= exponent,
+	 or 1.0 <= x < 2^2^i and exponent >= MIN_EXP - 1.  */
+
+      if (x < L_(1.0))
+	/* Invariants: x * 2^exponent = argument, x < 1.0 and
+	   exponent - 2^i < MIN_EXP - 1 <= exponent.  */
+	while (i > 0)
+	  {
+	    i--;
+	    if (exponent - (1 << i) >= MIN_EXP - 1)
+	      {
+		exponent -= (1 << i);
+		x *= pow2[i];
+		if (x >= L_(1.0))
+		  break;
+	      }
+	  }
+
+      /* Here either x < 1.0 and exponent = MIN_EXP - 1,
+	 or 1.0 <= x < 2^2^i and exponent >= MIN_EXP - 1.  */
+    }
+
+  /* Invariants: x * 2^exponent = argument, and
+     either x < 1.0 and exponent = MIN_EXP - 1,
+     or 1.0 <= x < 2^2^i and exponent >= MIN_EXP - 1.  */
+  while (i > 0)
+    {
+      i--;
+      if (x >= pow2[i])
+	{
+	  exponent += (1 << i);
+	  x *= powh[i];
+	}
+    }
+  /* Here either x < 1.0 and exponent = MIN_EXP - 1,
+     or 1.0 <= x < 2.0 and exponent >= MIN_EXP - 1.  */
+# endif
+
+  *exp = exponent;
+  return x;
+}
+
+#else
+
+/* This declaration is solely to ensure that after preprocessing
+   this file is never empty.  */
+typedef int dummy;
+
+#endif

new file mode 100644
--- /dev/null
+++ b/lib/printf-frexp.h
@@ -0,0 +1,24 @@
+/* Split a double into fraction and mantissa, for hexadecimal printf.
+   Copyright (C) 2007 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 2, 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, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* Write a finite, positive number x as
+     x = mantissa * 2^exp
+   where exp >= DBL_MIN_EXP - 1,
+         mantissa < 2.0,
+         if x is not a denormalized number then mantissa >= 1.0.
+   Store exp and return mantissa.  */
+extern double printf_frexp (double x, int *exp);

new file mode 100644
--- /dev/null
+++ b/m4/printf-frexp.m4
@@ -0,0 +1,40 @@
+# printf-frexp.m4 serial 1
+dnl Copyright (C) 2007 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.
+
+dnl Check how to define printf_frexp() without linking with libm.
+
+AC_DEFUN([gl_FUNC_PRINTF_FREXP],
+[
+  AC_CACHE_CHECK([whether frexp can be used without linking with libm],
+    [gl_cv_func_frexp_no_libm],
+    [
+      AC_TRY_LINK([#include <math.h>
+                   double x;
+                   int y;],
+                  [return frexp (x, &y) < 1;],
+        [gl_cv_func_frexp_no_libm=yes],
+        [gl_cv_func_frexp_no_libm=no])
+    ])
+  if test $gl_cv_func_frexp_no_libm = yes; then
+    AC_DEFINE([HAVE_FREXP_IN_LIBC], 1,
+      [Define if the frexp function is available in libc.])
+  fi
+
+  AC_CACHE_CHECK([whether ldexp can be used without linking with libm],
+    [gl_cv_func_ldexp_no_libm],
+    [
+      AC_TRY_LINK([#include <math.h>
+                   double x;
+                   int y;],
+                  [return ldexp (x, y) < 1;],
+        [gl_cv_func_ldexp_no_libm=yes],
+        [gl_cv_func_ldexp_no_libm=no])
+    ])
+  if test $gl_cv_func_ldexp_no_libm = yes; then
+    AC_DEFINE([HAVE_LDEXP_IN_LIBC], 1,
+      [Define if the ldexp function is available in libc.])
+  fi
+])

new file mode 100644
--- /dev/null
+++ b/modules/printf-frexp
@@ -0,0 +1,27 @@
+Description:
+printf_frexp() function: split a double into fraction and mantissa, for
+hexadecimal printf, without requiring libm.
+
+Files:
+lib/printf-frexp.h
+lib/printf-frexp.c
+m4/printf-frexp.m4
+
+Depends-on:
+verify
+
+configure.ac:
+gl_FUNC_PRINTF_FREXP
+
+Makefile.am:
+lib_SOURCES += printf-frexp.c
+
+Include:
+#include "printf-frexp.h"
+
+License:
+LGPL
+
+Maintainer:
+Bruno Haible
+