math: rewrite modf.c and clean up modff.c

cleaner implementation with unions and unsigned arithmetic

src/math/modf.c

-/* origin: FreeBSD /usr/src/lib/msun/src/s_modf.c */
-/*
- * ====================================================
- * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
- *
- * Developed at SunPro, a Sun Microsystems, Inc. business.
- * Permission to use, copy, modify, and distribute this
- * software is freely granted, provided that this notice
- * is preserved.
- * ====================================================
- */
-/*
- * modf(double x, double *iptr)
- * return fraction part of x, and return x's integral part in *iptr.
- * Method:
- *      Bit twiddling.
- *
- * Exception:
- *      No exception.
- */
-
-#include "libm.h"
+#include <math.h>
+#include <stdint.h>
 
 double modf(double x, double *iptr)
 {
-	int32_t i0,i1,j0;
-	uint32_t i;
+	union {double x; uint64_t n;} u = {x};
+	uint64_t mask;
+	int e;
 
-	EXTRACT_WORDS(i0, i1, x);
-	j0 = ((i0>>20) & 0x7ff) - 0x3ff; /* exponent of x */
-	if (j0 < 20) {  /* integer part in high x */
-		if (j0 < 0) {  /* |x| < 1 */
-			INSERT_WORDS(*iptr, i0 & 0x80000000, 0); /* *iptr = +-0 */
-			return x;
-		}
-		i = 0x000fffff >> j0;
-		if (((i0&i)|i1) == 0) {  /* x is integral */
-			uint32_t high;
-			*iptr = x;
-			GET_HIGH_WORD(high, x);
-			INSERT_WORDS(x, high & 0x80000000, 0);  /* return +-0 */
-			return x;
-		}
-		INSERT_WORDS(*iptr, i0&~i, 0);
-		return x - *iptr;
-	} else if (j0 > 51) {  /* no fraction part */
-		uint32_t high;
-		if (j0 == 0x400) {  /* inf/NaN */
-			*iptr = x;
-			return 0.0 / x;
-		}
+	e = (int)(u.n>>52 & 0x7ff) - 0x3ff;
+
+	/* no fractional part */
+	if (e >= 52) {
 		*iptr = x;
-		GET_HIGH_WORD(high, x);
-		INSERT_WORDS(x, high & 0x80000000, 0);  /* return +-0 */
-		return x;
-	} else {               /* fraction part in low x */
-		i = (uint32_t)0xffffffff >> (j0 - 20);
-		if ((i1&i) == 0) {  /* x is integral */
-			uint32_t high;
-			*iptr = x;
-			GET_HIGH_WORD(high, x);
-			INSERT_WORDS(x, high & 0x80000000, 0);  /* return +-0 */
+		if (e == 0x400 && u.n<<12 != 0) /* nan */
 			return x;
-		}
-		INSERT_WORDS(*iptr, i0, i1&~i);
-		return x - *iptr;
+		u.n &= (uint64_t)1<<63;
+		return u.x;
+	}
+
+	/* no integral part*/
+	if (e < 0) {
+		u.n &= (uint64_t)1<<63;
+		*iptr = u.x;
+		return x;
+	}
+
+	mask = (uint64_t)-1>>12 >> e;
+	if ((u.n & mask) == 0) {
+		*iptr = x;
+		u.n &= (uint64_t)1<<63;
+		return u.x;
 	}
+	u.n &= ~mask;
+	*iptr = u.x;
+	return x - *iptr;
 }

src/math/modff.c

-#include "libm.h"
+#include <math.h>
+#include <stdint.h>
 
 float modff(float x, float *iptr)
 {
-	uint32_t u, mask;
+	union {float x; uint32_t n;} u = {x};
+	uint32_t mask;
 	int e;
 
-	GET_FLOAT_WORD(u, x);
-	e = (int)(u>>23 & 0xff) - 0x7f;
+	e = (int)(u.n>>23 & 0xff) - 0x7f;
 
 	/* no fractional part */
 	if (e >= 23) {
 		*iptr = x;
-		if (e == 0x80 && u<<9 != 0) /* nan */
+		if (e == 0x80 && u.n<<9 != 0) { /* nan */
 			return x;
-		SET_FLOAT_WORD(x, u & 0x80000000);
-		return x;
+		}
+		u.n &= 0x80000000;
+		return u.x;
 	}
 	/* no integral part */
 	if (e < 0) {
-		SET_FLOAT_WORD(*iptr, u & 0x80000000);
+		u.n &= 0x80000000;
+		*iptr = u.x;
 		return x;
 	}
 
 	mask = 0x007fffff>>e;
-	if ((u & mask) == 0) {
+	if ((u.n & mask) == 0) {
 		*iptr = x;
-		SET_FLOAT_WORD(x, u & 0x80000000);
-		return x;
+		u.n &= 0x80000000;
+		return u.x;
 	}
-	SET_FLOAT_WORD(*iptr, u & ~mask);
+	u.n &= ~mask;
+	*iptr = u.x;
 	return x - *iptr;
 }