ICU-315 add portable IEEEremainder implementation

X-SVN-Rev: 1066

icu4c/source/common/putil.c

@@ -405,8 +405,27 @@ uprv_IEEEremainder(double x, double p)
   
   return x;
 #else
-  /* {sfb} need to fix this*/
-  return uprv_fmod(x, p);
+    /* Portable implementation of IEEEremainder.  This implementation
+     * should work on platforms that do not have IEEE bit layouts.
+     * Deficiencies of this implementation are that it does not
+     * attempt to handle NaN or infinite parameters and it returns the
+     * dividend if the divisor is zero.  This is probably not an issue
+     * on non-IEEE platforms. - aliu
+     */
+    if (p == 0.0) { // zero divisor
+        return x;
+    }
+    double a = x / p;
+    double aint = uprv_floor(a);
+    double afrac = a - aint;
+    if (afrac > 0.5) {
+        aint += 1.0;
+    } else if (!(afrac < 0.5)) { // avoid == comparison
+        if (uprv_modf(aint / 2.0, &a) > 0.0) {
+            aint += 1.0;
+        }
+    }
+    return x - (p * aint);
 #endif
 }