Use integer fields for mp_bases logarithm tables.

1 files changed, 80 insertions, 18 deletions

diff --git a/gen-bases.c b/gen-bases.c
index 31895e8b2..a467c19eb 100644
--- a/gen-bases.c
+++ b/gen-bases.c
@@ -1,7 +1,7 @@
 /* Generate mp_bases data.
 
-Copyright 1991, 1993, 1994, 1996, 2000, 2002, 2004 Free Software Foundation,
-Inc.
+Copyright 1991, 1993, 1994, 1996, 2000, 2002, 2004, 2011 Free Software
+Foundation, Inc.
 
 This file is part of the GNU MP Library.
 
@@ -24,7 +24,6 @@ along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
 
 
 int    chars_per_limb;
-double chars_per_bit_exactly;
 mpz_t  big_base;
 int    normalization_steps;
 mpz_t  big_base_inverted;
@@ -59,8 +58,6 @@ generate (int limb_bits, int nail_bits, int base)
       chars_per_limb++;
     }
 
-  chars_per_bit_exactly = 0.69314718055994530942 / log ((double) base);
-
   mpz_ui_pow_ui (big_base, (long) base, (long) chars_per_limb);
 
   normalization_steps = limb_bits - mpz_sizeinbase (big_base, 2);
@@ -97,11 +94,61 @@ header (int limb_bits, int nail_bits)
   printf ("#define MP_BASES_NORMALIZATION_STEPS_10 %d\n", normalization_steps);
 }
 
+
+#define EXTRA 16
+
+/* Compute log(2)/log(b) as a fixnum. */
+void
+mp_2logb (mpz_t r, int bi, int prec)
+{
+  mpz_t t, t2, two, b;
+  int i;
+
+  mpz_init_set_ui (t, 1);
+  mpz_mul_2exp (t, t, prec+EXTRA);
+
+  mpz_init (t2);
+
+  mpz_init_set_ui (two, 2);
+  mpz_mul_2exp (two, two, prec+EXTRA);
+
+  mpz_set_ui (r, 0);
+
+  mpz_init_set_ui (b, bi);
+  mpz_mul_2exp (b, b, prec+EXTRA);
+
+  for (i = prec-1; i >= 0; i--)
+    {
+      mpz_mul_2exp (b, b, prec+EXTRA);
+      mpz_sqrt (b, b);
+
+      mpz_mul (t2, t, b);
+      mpz_tdiv_q_2exp (t2, t2, prec+EXTRA);
+
+      if (mpz_cmp (t2, two) < 0)	/* not too large? */
+	{
+	  mpz_setbit (r, i);		/* set next less significant bit */
+	  mpz_set (t, t2);		/* new value acceptable */
+	}
+    }
+
+  mpz_clear (t);
+  mpz_clear (t2);
+  mpz_clear (two);
+  mpz_clear (b);
+}
+
 void
 table (int limb_bits, int nail_bits)
 {
   int  numb_bits = limb_bits - nail_bits;
   int  base;
+  mpz_t r, t, logb2, log2b;
+
+  mpz_init (r);
+  mpz_init (t);
+  mpz_init (logb2);
+  mpz_init (log2b);
 
   printf ("/* This file generated by gen-bases.c - DO NOT EDIT. */\n");
   printf ("\n");
@@ -113,30 +160,45 @@ table (int limb_bits, int nail_bits)
   printf ("#endif\n");
   printf ("\n");
   puts ("const struct bases mp_bases[257] =\n{");
-  puts ("  /*   0 */ { 0, 0.0, 0 },");
-  puts ("  /*   1 */ { 0, 1e37, 0 },");
+  puts ("  /*   0 */ { 0, 0.0,  0, 0, 0, 0 },");
+  puts ("  /*   1 */ { 0, 1e37, 0, 0, 0, 0 },");
   for (base = 2; base <= 256; base++)
     {
       generate (limb_bits, nail_bits, base);
+      mp_2logb (r, base, limb_bits + 8);
+      mpz_tdiv_q_2exp (logb2, r, 8);
+      mpz_set_ui (t, 1);
+      mpz_mul_2exp (t, t, 2*limb_bits + 5);
+      mpz_sub_ui (t, t, 1);
+      mpz_add_ui (r, r, 1);
+      mpz_tdiv_q (log2b, t, r);
 
       printf ("  /* %3u */ { ", base);
       if (POW2_P (base))
 	{
-          printf ("%u, %.16f, 0x%x },\n",
-                  chars_per_limb, chars_per_bit_exactly, ulog2 (base) - 1);
-	}
-      else
-	{
-          printf ("%u, %.16f, CNST_LIMB(0x",
-                  chars_per_limb, chars_per_bit_exactly);
-	  mpz_out_str (stdout, 16, big_base);
-          printf ("), CNST_LIMB(0x");
-	  mpz_out_str (stdout, 16, big_base_inverted);
-          printf (") },\n");
+          mpz_set_ui (big_base, ulog2 (base) - 1);
+	  mpz_set_ui (big_base_inverted, 0);
 	}
+
+      printf ("%u,", chars_per_limb);
+      printf (" CNST_LIMB(0x");
+      mpz_out_str (stdout, 16, logb2);
+      printf ("), CNST_LIMB(0x");
+      mpz_out_str (stdout, 16, log2b);
+      printf ("), CNST_LIMB(0x");
+      mpz_out_str (stdout, 16, big_base);
+      printf ("), CNST_LIMB(0x");
+      mpz_out_str (stdout, 16, big_base_inverted);
+      printf (") },\n");
     }
 
   puts ("};");
+
+  mpz_clear (r);
+  mpz_clear (t);
+  mpz_clear (logb2);
+  mpz_clear (log2b);
+
 }
 
 int