[pure-lang-svn] SF.net SVN: pure-lang: [370] pure/trunk

[<ag...@us...>]

Revision: 370
          http://pure-lang.svn.sourceforge.net/pure-lang/?rev=370&view=rev
Author:   agraef
Date:     2008-07-02 13:46:27 -0700 (Wed, 02 Jul 2008)

Log Message:
-----------
Add double->rational conversion.

Modified Paths:
--------------
    pure/trunk/lib/math.pure
    pure/trunk/runtime.cc
    pure/trunk/runtime.h

Modified: pure/trunk/lib/math.pure
===================================================================
--- pure/trunk/lib/math.pure	2008-07-02 19:26:25 UTC (rev 369)
+++ pure/trunk/lib/math.pure	2008-07-02 20:46:27 UTC (rev 370)
@@ -418,12 +418,16 @@
 
 /* Conversions. */
 
+extern expr* pure_rational(double);
+
 rational x@(_%_)	= x;
 rational x::int		|
 rational x::bigint	= x%1;
 
-// TODO: Need to rationalize doubles here. Currently this is a no-op.
-rational x::double	= x;
+/* The conversion from double doesn't do any rounding, so it is guaranteed
+   that converting the resulting rational back to double reconstructs the
+   original value. */
+rational x::double	= n%d when n,d = pure_rational x end;
 
 rational (x+:y)	= rational x +: rational y;
 rational (x<:y)	= rational x <: rational y;

Modified: pure/trunk/runtime.cc
===================================================================
--- pure/trunk/runtime.cc	2008-07-02 19:26:25 UTC (rev 369)
+++ pure/trunk/runtime.cc	2008-07-02 20:46:27 UTC (rev 370)
@@ -1786,6 +1786,22 @@
 }
 
 extern "C"
+pure_expr *pure_rational(double d)
+{
+  pure_expr *u = pure_bigint(0, 0);
+  pure_expr *v = pure_bigint(0, 0);
+  mpz_t& x = u->data.z;
+  mpz_t& y = v->data.z;
+  mpq_t q;
+  mpq_init(q);
+  mpq_set_d(q, d);
+  mpq_get_num(x, q);
+  mpq_get_den(y, q);
+  mpq_clear(q);
+  return pure_tuplel(2, u, v);
+}
+
+extern "C"
 pure_expr *bigint_neg(mpz_t x)
 {
   pure_expr *u = pure_bigint(0, 0);

Modified: pure/trunk/runtime.h
===================================================================
--- pure/trunk/runtime.h	2008-07-02 19:26:25 UTC (rev 369)
+++ pure/trunk/runtime.h	2008-07-02 20:46:27 UTC (rev 370)
@@ -415,6 +415,11 @@
 pure_expr *pure_bigintval(pure_expr *x);
 pure_expr *pure_pointerval(pure_expr *x);
 
+/* Convert a double to a rational number, without rounding. Returns a pair n,d
+   of two bigint values, where n is the numerator and d the denominator. */
+
+pure_expr *pure_rational(double d);
+
 /* Construct a "byte string" from a string. The result is a raw pointer object
    pointing to the converted string. The original string is copied (and, in
    the case of pure_byte_cstring, converted to the system encoding). The


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