set a mpfr from an integer

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@27 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 74 insertions, 0 deletions

diff --git a/set_z.c b/set_z.c
new file mode 100644
index 000000000..cf6ee0899
--- /dev/null
+++ b/set_z.c
@@ -0,0 +1,74 @@
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+#include "mpfr.h"
+
+/* set f to the integer z */
+int mpfr_set_z (f, z, rnd) mpfr_ptr f; mpz_srcptr z; 
+unsigned char rnd;
+{
+  int fn, zn, k, dif, sign_z, sh; mp_limb_t *fp = MANT(f), cc, c2;
+
+  sign_z = mpz_cmp_ui(z,0);
+  if (sign_z==0) return (SIZE(f)=0);
+  fn = 1 + (PREC(f)-1)/mp_bits_per_limb;
+  zn = SIZ(z);
+  dif = zn-fn;
+  count_leading_zeros(k, PTR(z)[zn-1]);
+  EXP(f) = zn*mp_bits_per_limb-k;
+  if (SIGN(f)*sign_z<0) CHANGE_SIGN(f);
+  if (dif>=0) { /* number has to be truncated */
+    if (k) {
+      mpn_lshift(fp, PTR(z) + dif, fn, k);
+      if (dif) *fp += PTR(z)[dif-1] >> (mp_bits_per_limb-k);
+    }
+    else MPN_COPY(fp, PTR(z) + dif, fn);
+    sh = fn*mp_bits_per_limb-PREC(f);
+    cc = *fp & (((mp_limb_t)1 << sh) - 1);
+    *fp = *fp & ~cc;
+    if (rnd==GMP_RNDN) {
+      if (sh) c2 = (mp_limb_t)1 << (sh-1);
+      else { /* sh=0 */
+	c2 = (mp_limb_t)1 << (mp_bits_per_limb-1);
+	dif--;
+	cc = (dif>=0) ? PTR(z)[dif] : 0;
+      }
+      /* now compares cc to c2 */
+      if (cc>c2) { mpfr_add_one_ulp(f); return cc; }
+      else if (cc<c2) goto towards_zero;
+      else {
+	cc=0;
+	while (dif>0 && (cc=PTR(z)[dif-1])==0) dif--;
+	if (cc) { mpfr_add_one_ulp(f); return cc; }
+	else /* exactly in middle: inexact in both cases */
+	  if (*fp & ((mp_limb_t)1<<sh)) { mpfr_add_one_ulp(f); return 1; }
+	  else return 1;
+      }
+    }
+    else if ((sign_z>0 && rnd==GMP_RNDU) || (sign_z<0 && rnd==GMP_RNDD)) {
+      /* round towards infinity */
+      /* result is exact iff all remaining bits are zero */
+      if (dif>0 && cc==0) cc=PTR(z)[--dif]<<k;
+      while (cc==0 && dif>0) cc=PTR(z)[--dif];
+      if (cc) { mpfr_add_one_ulp(f); return 1; }
+      else return 0;
+    }
+    else { /* round towards zero */
+      /* result is exact iff all remaining bits are zero */
+    towards_zero:
+      if (cc==0 && dif>0) cc=PTR(z)[--dif]<<k;
+      while (cc==0 && dif>0) cc=PTR(z)[--dif];
+      return cc;
+    }
+  }
+  else {
+    if (k) mpn_lshift(fp-dif, PTR(z), zn, k);
+    else MPN_COPY(fp-dif, PTR(z), zn);
+    /* fill with zeroes */
+    MPN_ZERO(fp, -dif);
+    return 0; /* result is exact */
+  }
+}
+
+
+