Remove Paolo's variant of the algorithm, with his permission.

diff --git a/ChangeLog b/ChangeLog
index b84bd1c..b280df2 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2007-03-22  Bruno Haible  <bruno@clisp.org>
+
+       * lib/frexp.c: Remove older implementation that uses divisions.
+
 2007-03-21  Bruno Haible  <bruno@clisp.org>
 
        * modules/frexp-tests: New file.

diff --git a/lib/frexp.c b/lib/frexp.c
index b4b9f83..3074f2e 100644 (file)
--- a/lib/frexp.c
+++ b/lib/frexp.c
@@ -15,6 +15,9 @@
    with this program; if not, write to the Free Software Foundation,
    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
 
+/* Written by Paolo Bonzini <bonzini@gnu.org>, 2003, and
+   Bruno Haible <bruno@clisp.org>, 2007.  */
+
 #include <config.h>
 
 #if !(defined USE_LONG_DOUBLE && !HAVE_LONG_DOUBLE)
@@ -65,129 +68,86 @@ FUNC (DOUBLE x, int *exp)
       sign = -1;
     }
 
-  if (0)
-    {
-      /* Implementation contributed by Paolo Bonzini.
-         Disabled because it's under GPL and doesn't pass the tests.  */
-
-      /* Since the exponent is an 'int', it fits in 64 bits.  Therefore the
-        loops are executed no more than 64 times.  */
-      DOUBLE exponents[64];
-      DOUBLE *next;
-      int bit;
-
-      exponent = 0;
-      if (x >= L_(1.0))
-       {
-         for (next = exponents, exponents[0] = L_(2.0), bit = 1;
-              *next <= x + x;
-              bit <<= 1, next[1] = next[0] * next[0], next++);
-
-         for (; next >= exponents; bit >>= 1, next--)
-           if (x + x >= *next)
+  {
+    /* 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 positive 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)
              {
-               x /= *next;
-               exponent |= bit;
+               exponent += (1 << i);
+               x *= powh_i;
              }
-       }
-      else if (x < L_(0.5))
-       {
-         for (next = exponents, exponents[0] = L_(0.5), bit = 1;
-              *next > x;
-              bit <<= 1, next[1] = next[0] * next[0], next++);
-
-         for (; next >= exponents; bit >>= 1, next--)
-           if (x < *next)
+           else
+             break;
+
+           pow2[i] = pow2_i;
+           powh[i] = powh_i;
+         }
+       /* Avoid making x too small, as it could become a denormalized
+          number and thus lose precision.  */
+       while (i > 0 && x < pow2[i - 1])
+         {
+           i--;
+           powh_i = powh[i];
+         }
+       exponent += (1 << i);
+       x *= powh_i;
+       /* Here 2^-2^i <= x < 1.0.  */
+      }
+    else
+      {
+       /* A negative or zero 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 < powh_i)
              {
-               x /= *next;
-               exponent |= bit;
+               exponent -= (1 << i);
+               x *= pow2_i;
              }
-         exponent = - exponent;
-       }
-    }
-  else
-    {
-      /* Implementation contributed by Bruno Haible.  */
-
-      /* 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 positive 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;
-           }
-         /* Avoid making x too small, as it could become a denormalized
-            number and thus lose precision.  */
-         while (i > 0 && x < pow2[i - 1])
-           {
-             i--;
-             powh_i = powh[i];
-           }
-         exponent += (1 << i);
-         x *= powh_i;
-         /* Here 2^-2^i <= x < 1.0.  */
-       }
-      else
-       {
-         /* A negative or zero 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 < powh_i)
-               {
-                 exponent -= (1 << i);
-                 x *= pow2_i;
-               }
-             else
-               break;
-
-             pow2[i] = pow2_i;
-             powh[i] = powh_i;
-           }
-         /* Here 2^-2^i <= x < 1.0.  */
-       }
-
-      /* Invariants: x * 2^exponent = argument, and 2^-2^i <= x < 1.0.  */
-      while (i > 0)
-       {
-         i--;
-         if (x < powh[i])
-           {
-             exponent -= (1 << i);
-             x *= pow2[i];
-           }
-       }
-      /* Here 0.5 <= x < 1.0.  */
-    }
+           else
+             break;
+
+           pow2[i] = pow2_i;
+           powh[i] = powh_i;
+         }
+       /* Here 2^-2^i <= x < 1.0.  */
+      }
+
+    /* Invariants: x * 2^exponent = argument, and 2^-2^i <= x < 1.0.  */
+    while (i > 0)
+      {
+       i--;
+       if (x < powh[i])
+         {
+           exponent -= (1 << i);
+           x *= pow2[i];
+         }
+      }
+    /* Here 0.5 <= x < 1.0.  */
+  }
 
   *exp = exponent;
   return (sign < 0 ? - x : x);