added new macro MPFR_ALIAS

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@4947 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 17 insertions, 0 deletions

diff --git a/mpfr-impl.h b/mpfr-impl.h
index b44ff9b50..212bf572e 100644
--- a/mpfr-impl.h
+++ b/mpfr-impl.h
@@ -954,6 +954,23 @@ do {                                                                  \
 /* Needs <locale.h> */
 #define MPFR_DECIMAL_POINT ((unsigned char) localeconv()->decimal_point[0])
 
+/* Set y to s*significand(x)*2^e, for example MPFR_ALIAS(y,x,1,MPFR_EXP(x))
+   sets y to |x|, and MPFR_ALIAS(y,x,MPFR_SIGN(x),0) sets y to x*2^f such
+   that 1/2 <= |y| < 1. Does not check y is in the valid exponent range. 
+   WARNING! x and y share the same mantissa. So, some operations are
+   not valid if x has been provided via an argument, e.g., trying to
+   modify the mantissa of y, even temporarily, or calling mpfr_clear on y.
+*/
+#define MPFR_ALIAS(y,x,s,e)                     \
+  do                                            \
+    {                                           \
+      MPFR_PREC(y) = MPFR_PREC(x);              \
+      MPFR_SIGN(y) = (s);                       \
+      MPFR_EXP(y) = (e);                        \
+      MPFR_MANT(y) = MPFR_MANT(x);              \
+    } while (0)  
+
+
 /******************************************************
  **************  Save exponent macros  ****************
  ******************************************************/