New, improved fmod.c

lang/cem/libcc.ansi/math/fmod.c

@@ -1,33 +1,34 @@
-/*
- * (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
- * See the copyright notice in the ACK home directory, in the file "Copyright".
- *
- * Author: Hans van Eck
- */
+/* fmod function */
+/* Author Robert R. Hall (hall@crach.cts.com) */
+
 /* $Header$ */
 
-#include	<math.h>
-#include	<errno.h>
+#include <math.h>
+#include <errno.h>
 
 double
-fmod(double x, double y)
-{
-	double val;
-	double frac;
+(fmod)(double x, double y)
+{				/* compute fmod(x, y) */
+	double t;
+	int n, neg;
+	int ychar, xchar;
 
-	if (y == 0) {
+    	if (y == 0.0) {
 		errno = EDOM;
-		return 0;
-	}
-	frac = modf( x / y, &val);
+		return 0.0;
+    	}
+    				/* fmod(finite, finite) */
+	if (y < 0.0) y = -y;
+	if (x < 0.0) x = -x, neg = 1;
+	else neg = 0;
+	t = frexp(y, &ychar);
+				/* substract |y| until |x| < |y| */
 
-	return frac * y;
-
-/*
-	val = x / y;
-	if (val > LONG_MIN && val < LONG_MAX) {
-		long i = val;
-		return x - i * y;
+	t = frexp(x, &xchar);
+	for (n = xchar - ychar; 0 <= n; --n) {
+				/* try to substract |y|*2^n */
+	    t = ldexp(y, n);
+	    if (t <= x) x -= t;
 	}
-*/
+	return (neg ? -x : x);
 }