added static to local functions

explained threshold


git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@1505 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 45 insertions, 33 deletions

diff --git a/log2.c b/log2.c
index 286644fbc..21d5edc4a 100644
--- a/log2.c
+++ b/log2.c
@@ -30,8 +30,8 @@ mpfr_t __mpfr_const_log2; /* stored value of log(2) */
 int __mpfr_const_log2_prec=0; /* precision of stored value */
 mp_rnd_t __mpfr_const_log2_rnd; /* rounding mode of stored value */
 
-int mpfr_aux_log2 _PROTO ((mpfr_ptr, mpz_srcptr, int, int));
-int mpfr_const_aux_log2 _PROTO ((mpfr_ptr, mp_rnd_t));
+static int mpfr_aux_log2 _PROTO ((mpfr_ptr, mpz_srcptr, int, int));
+static int mpfr_const_aux_log2 _PROTO ((mpfr_ptr, mp_rnd_t));
 
 #define A
 #define A1 1
@@ -53,7 +53,7 @@ int mpfr_const_aux_log2 _PROTO ((mpfr_ptr, mp_rnd_t));
 #undef C1
 #undef C2
 
-int
+static int
 #if __STDC__
 mpfr_const_aux_log2 (mpfr_ptr mylog, mp_rnd_t rnd_mode)
 #else
@@ -112,6 +112,11 @@ mpfr_const_aux_log2 (mylog, rnd_mode)
   return 0;
 }
 
+/* Cross-over point from nai"ve Taylor series to binary splitting,
+   obtained experimentally on a Pentium II. Optimal value for
+   target machine should be determined by tuneup. */
+#define LOG2_THRESHOLD 25000
+
 /* set x to log(2) rounded to precision MPFR_PREC(x) with direction rnd_mode 
 
    use formula log(2) = sum(1/k/2^k, k=1..infinity)
@@ -147,38 +152,45 @@ mpfr_const_log2 (x, rnd_mode) mpfr_ptr x; mp_rnd_t rnd_mode;
   }
 
   /* need to recompute */
-  if (precx < 30000){ /* use nai"ve Taylor series evaluation */
-     N=2;
-     do {
-       oldN = N;
-       N = precx + _mpfr_ceil_log2 ((double) N);
-     } while (N != oldN);
-     mpz_init (s); /* set to zero */
-     mpz_init (u);
-     mpz_init_set_ui (t, 1);
-
-     /* use log(2) = sum((6*k-1)/(2*k^2-k)/2^(2*k+1), k=1..infinity) */
-     mpz_mul_2exp (t, t, N-1);
-     for (k=1; k<N/2; k++) {
-       mpz_div_2exp (t, t, 2);
-       mpz_mul_ui (u, t, 6*k-1);
-       mpz_fdiv_q_ui (u, u, k*(2*k-1));
-       mpz_add (s, s, u);
-     }
-
-     mpfr_set_z(x, s, rnd_mode);
-     MPFR_EXP(x) -= N;
-     mpz_clear(s); mpz_clear(t); mpz_clear(u);
-  } else
+  if (precx < LOG2_THRESHOLD) /* use nai"ve Taylor series evaluation */
     {
-      /* use binary splitting method */
-      mpfr_const_aux_log2(x, rnd_mode);
+      N=2;
+      do
+        {
+          oldN = N;
+          N = precx + _mpfr_ceil_log2 ((double) N);
+        }
+      while (N != oldN);
+      mpz_init (s); /* set to zero */
+      mpz_init (u);
+      mpz_init_set_ui (t, 1);
+
+      /* use log(2) = sum((6*k-1)/(2*k^2-k)/2^(2*k+1), k=1..infinity) */
+      mpz_mul_2exp (t, t, N-1);
+      for (k=1; k<N/2; k++)
+        {
+          mpz_div_2exp (t, t, 2);
+          mpz_mul_ui (u, t, 6*k-1);
+          mpz_fdiv_q_ui (u, u, k*(2*k-1));
+          mpz_add (s, s, u);
+        }
+
+      mpfr_set_z (x, s, rnd_mode);
+      MPFR_EXP(x) -= N;
+      mpz_clear (s);
+      mpz_clear (t);
+      mpz_clear (u);
     }
+  else /* use binary splitting method */
+    mpfr_const_aux_log2(x, rnd_mode);
 
   /* store computed value */
-  if (__mpfr_const_log2_prec==0) mpfr_init2(__mpfr_const_log2, precx);
-  else mpfr_set_prec(__mpfr_const_log2, precx);
-  mpfr_set(__mpfr_const_log2, x, rnd_mode);
-  __mpfr_const_log2_prec=precx;
-  __mpfr_const_log2_rnd=rnd_mode;
+  if (__mpfr_const_log2_prec == 0)
+    mpfr_init2 (__mpfr_const_log2, precx);
+  else
+    mpfr_set_prec (__mpfr_const_log2, precx);
+
+  mpfr_set (__mpfr_const_log2, x, rnd_mode);
+  __mpfr_const_log2_prec = precx;
+  __mpfr_const_log2_rnd = rnd_mode;
 }