From: Szabolcs Nagy <nsz@port70.net>
Date: Tue, 28 Oct 2014 23:34:37 +0000 (+0100)
Subject: math: use the rounding idiom consistently
X-Git-Tag: v1.1.6~61
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=0ce946cf808274c2d6e5419b139e130c8ad4bd30;p=oweals%2Fmusl.git

math: use the rounding idiom consistently

the idiomatic rounding of x is

  n = x + toint - toint;

where toint is either 1/EPSILON (x is non-negative) or 1.5/EPSILON
(x may be negative and nearest rounding mode is assumed) and EPSILON is
according to the evaluation precision (the type of toint is not very
important, because single precision float can represent the 1/EPSILON of
ieee binary128).

in case of FLT_EVAL_METHOD!=0 this avoids a useless store to double or
float precision, and the long double code became cleaner with
1/LDBL_EPSILON instead of ifdefs for toint.

__rem_pio2f and __rem_pio2 functions slightly changed semantics:
on i386 a double-rounding is avoided so close to half-way cases may
get evaluated differently eg. as sin(pi/4-eps) instead of cos(pi/4+eps)
---

diff --git a/src/math/__rem_pio2.c b/src/math/__rem_pio2.c
index 5fafc4a8..a40db9fc 100644
--- a/src/math/__rem_pio2.c
+++ b/src/math/__rem_pio2.c
@@ -19,6 +19,12 @@
 
 #include "libm.h"
 
+#if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
+#define EPS DBL_EPSILON
+#elif FLT_EVAL_METHOD==2
+#define EPS LDBL_EPSILON
+#endif
+
 /*
  * invpio2:  53 bits of 2/pi
  * pio2_1:   first  33 bit of pi/2
@@ -29,6 +35,7 @@
  * pio2_3t:  pi/2 - (pio2_1+pio2_2+pio2_3)
  */
 static const double
+toint   = 1.5/EPS,
 invpio2 = 6.36619772367581382433e-01, /* 0x3FE45F30, 0x6DC9C883 */
 pio2_1  = 1.57079632673412561417e+00, /* 0x3FF921FB, 0x54400000 */
 pio2_1t = 6.07710050650619224932e-11, /* 0x3DD0B461, 0x1A626331 */
@@ -41,8 +48,8 @@ pio2_3t = 8.47842766036889956997e-32; /* 0x397B839A, 0x252049C1 */
 int __rem_pio2(double x, double *y)
 {
 	union {double f; uint64_t i;} u = {x};
-	double_t z,w,t,r;
-	double tx[3],ty[2],fn;
+	double_t z,w,t,r,fn;
+	double tx[3],ty[2];
 	uint32_t ix;
 	int sign, n, ex, ey, i;
 
@@ -111,8 +118,7 @@ int __rem_pio2(double x, double *y)
 	if (ix < 0x413921fb) {  /* |x| ~< 2^20*(pi/2), medium size */
 medium:
 		/* rint(x/(pi/2)), Assume round-to-nearest. */
-		fn = x*invpio2 + 0x1.8p52;
-		fn = fn - 0x1.8p52;
+		fn = x*invpio2 + toint - toint;
 		n = (int32_t)fn;
 		r = x - fn*pio2_1;
 		w = fn*pio2_1t;  /* 1st round, good to 85 bits */
diff --git a/src/math/__rem_pio2f.c b/src/math/__rem_pio2f.c
index 838e1fca..f5163856 100644
--- a/src/math/__rem_pio2f.c
+++ b/src/math/__rem_pio2f.c
@@ -22,12 +22,19 @@
 
 #include "libm.h"
 
+#if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
+#define EPS DBL_EPSILON
+#elif FLT_EVAL_METHOD==2
+#define EPS LDBL_EPSILON
+#endif
+
 /*
  * invpio2:  53 bits of 2/pi
  * pio2_1:   first 25 bits of pi/2
  * pio2_1t:  pi/2 - pio2_1
  */
 static const double
+toint   = 1.5/EPS,
 invpio2 = 6.36619772367581382433e-01, /* 0x3FE45F30, 0x6DC9C883 */
 pio2_1  = 1.57079631090164184570e+00, /* 0x3FF921FB, 0x50000000 */
 pio2_1t = 1.58932547735281966916e-08; /* 0x3E5110b4, 0x611A6263 */
@@ -35,7 +42,8 @@ pio2_1t = 1.58932547735281966916e-08; /* 0x3E5110b4, 0x611A6263 */
 int __rem_pio2f(float x, double *y)
 {
 	union {float f; uint32_t i;} u = {x};
-	double tx[1],ty[1],fn;
+	double tx[1],ty[1];
+	double_t fn;
 	uint32_t ix;
 	int n, sign, e0;
 
@@ -43,8 +51,7 @@ int __rem_pio2f(float x, double *y)
 	/* 25+53 bit pi is good enough for medium size */
 	if (ix < 0x4dc90fdb) {  /* |x| ~< 2^28*(pi/2), medium size */
 		/* Use a specialized rint() to get fn.  Assume round-to-nearest. */
-		fn = x*invpio2 + 0x1.8p52;
-		fn = fn - 0x1.8p52;
+		fn = x*invpio2 + toint - toint;
 		n  = (int32_t)fn;
 		*y = x - fn*pio2_1 - fn*pio2_1t;
 		return n;
diff --git a/src/math/__rem_pio2l.c b/src/math/__rem_pio2l.c
index 8b15b7b2..77255bd8 100644
--- a/src/math/__rem_pio2l.c
+++ b/src/math/__rem_pio2l.c
@@ -20,10 +20,11 @@
  * use __rem_pio2_large() for large x
  */
 
+static const long double toint = 1.5/LDBL_EPSILON;
+
 #if LDBL_MANT_DIG == 64
 /* u ~< 0x1p25*pi/2 */
 #define SMALL(u) (((u.i.se & 0x7fffU)<<16 | u.i.m>>48) < ((0x3fff + 25)<<16 | 0x921f>>1 | 0x8000))
-#define TOINT 0x1.8p63
 #define QUOBITS(x) ((uint32_t)(int32_t)x & 0x7fffffff)
 #define ROUND1 22
 #define ROUND2 61
@@ -50,7 +51,6 @@ pio2_3t = -2.75299651904407171810e-37L; /* -0xbb5bf6c7ddd660ce.0p-185 */
 #elif LDBL_MANT_DIG == 113
 /* u ~< 0x1p45*pi/2 */
 #define SMALL(u) (((u.i.se & 0x7fffU)<<16 | u.i.top) < ((0x3fff + 45)<<16 | 0x921f))
-#define TOINT 0x1.8p112
 #define QUOBITS(x) ((uint32_t)(int64_t)x & 0x7fffffff)
 #define ROUND1 51
 #define ROUND2 119
@@ -77,7 +77,7 @@ int __rem_pio2l(long double x, long double *y)
 	ex = u.i.se & 0x7fff;
 	if (SMALL(u)) {
 		/* rint(x/(pi/2)), Assume round-to-nearest. */
-		fn = x*invpio2 + TOINT - TOINT;
+		fn = x*invpio2 + toint - toint;
 		n = QUOBITS(fn);
 		r = x-fn*pio2_1;
 		w = fn*pio2_1t;  /* 1st round good to 102/180 bits (ld80/ld128) */
diff --git a/src/math/ceil.c b/src/math/ceil.c
index 22dc224c..b13e6f2d 100644
--- a/src/math/ceil.c
+++ b/src/math/ceil.c
@@ -1,5 +1,12 @@
 #include "libm.h"
 
+#if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
+#define EPS DBL_EPSILON
+#elif FLT_EVAL_METHOD==2
+#define EPS LDBL_EPSILON
+#endif
+static const double_t toint = 1/EPS;
+
 double ceil(double x)
 {
 	union {double f; uint64_t i;} u = {x};
@@ -10,9 +17,9 @@ double ceil(double x)
 		return x;
 	/* y = int(x) - x, where int(x) is an integer neighbor of x */
 	if (u.i >> 63)
-		y = (double)(x - 0x1p52) + 0x1p52 - x;
+		y = x - toint + toint - x;
 	else
-		y = (double)(x + 0x1p52) - 0x1p52 - x;
+		y = x + toint - toint - x;
 	/* special case because of non-nearest rounding modes */
 	if (e <= 0x3ff-1) {
 		FORCE_EVAL(y);
diff --git a/src/math/ceill.c b/src/math/ceill.c
index a2cb0a7f..60a83020 100644
--- a/src/math/ceill.c
+++ b/src/math/ceill.c
@@ -6,11 +6,9 @@ long double ceill(long double x)
 	return ceil(x);
 }
 #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
-#if LDBL_MANT_DIG == 64
-#define TOINT 0x1p63
-#elif LDBL_MANT_DIG == 113
-#define TOINT 0x1p112
-#endif
+
+static const long double toint = 1/LDBL_EPSILON;
+
 long double ceill(long double x)
 {
 	union ldshape u = {x};
@@ -21,9 +19,9 @@ long double ceill(long double x)
 		return x;
 	/* y = int(x) - x, where int(x) is an integer neighbor of x */
 	if (u.i.se >> 15)
-		y = x - TOINT + TOINT - x;
+		y = x - toint + toint - x;
 	else
-		y = x + TOINT - TOINT - x;
+		y = x + toint - toint - x;
 	/* special case because of non-nearest rounding modes */
 	if (e <= 0x3fff-1) {
 		FORCE_EVAL(y);
diff --git a/src/math/floor.c b/src/math/floor.c
index ebc9fabe..14a31cd8 100644
--- a/src/math/floor.c
+++ b/src/math/floor.c
@@ -1,5 +1,12 @@
 #include "libm.h"
 
+#if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
+#define EPS DBL_EPSILON
+#elif FLT_EVAL_METHOD==2
+#define EPS LDBL_EPSILON
+#endif
+static const double_t toint = 1/EPS;
+
 double floor(double x)
 {
 	union {double f; uint64_t i;} u = {x};
@@ -10,9 +17,9 @@ double floor(double x)
 		return x;
 	/* y = int(x) - x, where int(x) is an integer neighbor of x */
 	if (u.i >> 63)
-		y = (double)(x - 0x1p52) + 0x1p52 - x;
+		y = x - toint + toint - x;
 	else
-		y = (double)(x + 0x1p52) - 0x1p52 - x;
+		y = x + toint - toint - x;
 	/* special case because of non-nearest rounding modes */
 	if (e <= 0x3ff-1) {
 		FORCE_EVAL(y);
diff --git a/src/math/floorl.c b/src/math/floorl.c
index 961f9e89..16aaec48 100644
--- a/src/math/floorl.c
+++ b/src/math/floorl.c
@@ -6,11 +6,9 @@ long double floorl(long double x)
 	return floor(x);
 }
 #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
-#if LDBL_MANT_DIG == 64
-#define TOINT 0x1p63
-#elif LDBL_MANT_DIG == 113
-#define TOINT 0x1p112
-#endif
+
+static const long double toint = 1/LDBL_EPSILON;
+
 long double floorl(long double x)
 {
 	union ldshape u = {x};
@@ -21,9 +19,9 @@ long double floorl(long double x)
 		return x;
 	/* y = int(x) - x, where int(x) is an integer neighbor of x */
 	if (u.i.se >> 15)
-		y = x - TOINT + TOINT - x;
+		y = x - toint + toint - x;
 	else
-		y = x + TOINT - TOINT - x;
+		y = x + toint - toint - x;
 	/* special case because of non-nearest rounding modes */
 	if (e <= 0x3fff-1) {
 		FORCE_EVAL(y);
diff --git a/src/math/modfl.c b/src/math/modfl.c
index 4b03a4be..a47b1924 100644
--- a/src/math/modfl.c
+++ b/src/math/modfl.c
@@ -11,11 +11,9 @@ long double modfl(long double x, long double *iptr)
 	return r;
 }
 #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
-#if LDBL_MANT_DIG == 64
-#define TOINT 0x1p63
-#elif LDBL_MANT_DIG == 113
-#define TOINT 0x1p112
-#endif
+
+static const long double toint = 1/LDBL_EPSILON;
+
 long double modfl(long double x, long double *iptr)
 {
 	union ldshape u = {x};
@@ -40,7 +38,7 @@ long double modfl(long double x, long double *iptr)
 
 	/* raises spurious inexact */
 	absx = s ? -x : x;
-	y = absx + TOINT - TOINT - absx;
+	y = absx + toint - toint - absx;
 	if (y == 0) {
 		*iptr = x;
 		return s ? -0.0 : 0.0;
diff --git a/src/math/rintl.c b/src/math/rintl.c
index 26725073..374327db 100644
--- a/src/math/rintl.c
+++ b/src/math/rintl.c
@@ -6,11 +6,9 @@ long double rintl(long double x)
 	return rint(x);
 }
 #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
-#if LDBL_MANT_DIG == 64
-#define TOINT 0x1p63
-#elif LDBL_MANT_DIG == 113
-#define TOINT 0x1p112
-#endif
+
+static const long double toint = 1/LDBL_EPSILON;
+
 long double rintl(long double x)
 {
 	union ldshape u = {x};
@@ -21,9 +19,9 @@ long double rintl(long double x)
 	if (e >= 0x3fff+LDBL_MANT_DIG-1)
 		return x;
 	if (s)
-		y = x - TOINT + TOINT;
+		y = x - toint + toint;
 	else
-		y = x + TOINT - TOINT;
+		y = x + toint - toint;
 	if (y == 0)
 		return 0*x;
 	return y;
diff --git a/src/math/round.c b/src/math/round.c
index 4b38d1fd..130d58d2 100644
--- a/src/math/round.c
+++ b/src/math/round.c
@@ -1,5 +1,12 @@
 #include "libm.h"
 
+#if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
+#define EPS DBL_EPSILON
+#elif FLT_EVAL_METHOD==2
+#define EPS LDBL_EPSILON
+#endif
+static const double_t toint = 1/EPS;
+
 double round(double x)
 {
 	union {double f; uint64_t i;} u = {x};
@@ -12,10 +19,10 @@ double round(double x)
 		x = -x;
 	if (e < 0x3ff-1) {
 		/* raise inexact if x!=0 */
-		FORCE_EVAL(x + 0x1p52);
+		FORCE_EVAL(x + toint);
 		return 0*u.f;
 	}
-	y = (double)(x + 0x1p52) - 0x1p52 - x;
+	y = x + toint - toint - x;
 	if (y > 0.5)
 		y = y + x - 1;
 	else if (y <= -0.5)
diff --git a/src/math/roundf.c b/src/math/roundf.c
index c6b27797..e8210af5 100644
--- a/src/math/roundf.c
+++ b/src/math/roundf.c
@@ -1,5 +1,14 @@
 #include "libm.h"
 
+#if FLT_EVAL_METHOD==0
+#define EPS FLT_EPSILON
+#elif FLT_EVAL_METHOD==1
+#define EPS DBL_EPSILON
+#elif FLT_EVAL_METHOD==2
+#define EPS LDBL_EPSILON
+#endif
+static const float_t toint = 1/EPS;
+
 float roundf(float x)
 {
 	union {float f; uint32_t i;} u = {x};
@@ -11,10 +20,10 @@ float roundf(float x)
 	if (u.i >> 31)
 		x = -x;
 	if (e < 0x7f-1) {
-		FORCE_EVAL(x + 0x1p23f);
+		FORCE_EVAL(x + toint);
 		return 0*u.f;
 	}
-	y = (float)(x + 0x1p23f) - 0x1p23f - x;
+	y = x + toint - toint - x;
 	if (y > 0.5f)
 		y = y + x - 1;
 	else if (y <= -0.5f)
diff --git a/src/math/roundl.c b/src/math/roundl.c
index 8f3f28b3..f4ff6820 100644
--- a/src/math/roundl.c
+++ b/src/math/roundl.c
@@ -6,11 +6,9 @@ long double roundl(long double x)
 	return round(x);
 }
 #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
-#if LDBL_MANT_DIG == 64
-#define TOINT 0x1p63
-#elif LDBL_MANT_DIG == 113
-#define TOINT 0x1p112
-#endif
+
+static const long double toint = 1/LDBL_EPSILON;
+
 long double roundl(long double x)
 {
 	union ldshape u = {x};
@@ -22,10 +20,10 @@ long double roundl(long double x)
 	if (u.i.se >> 15)
 		x = -x;
 	if (e < 0x3fff-1) {
-		FORCE_EVAL(x + TOINT);
+		FORCE_EVAL(x + toint);
 		return 0*u.f;
 	}
-	y = x + TOINT - TOINT - x;
+	y = x + toint - toint - x;
 	if (y > 0.5)
 		y = y + x - 1;
 	else if (y <= -0.5)
diff --git a/src/math/truncl.c b/src/math/truncl.c
index 3eedb083..f07b1934 100644
--- a/src/math/truncl.c
+++ b/src/math/truncl.c
@@ -6,11 +6,9 @@ long double truncl(long double x)
 	return trunc(x);
 }
 #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
-#if LDBL_MANT_DIG == 64
-#define TOINT 0x1p63
-#elif LDBL_MANT_DIG == 113
-#define TOINT 0x1p112
-#endif
+
+static const long double toint = 1/LDBL_EPSILON;
+
 long double truncl(long double x)
 {
 	union ldshape u = {x};
@@ -27,7 +25,7 @@ long double truncl(long double x)
 	/* y = int(|x|) - |x|, where int(|x|) is an integer neighbor of |x| */
 	if (s)
 		x = -x;
-	y = x + TOINT - TOINT - x;
+	y = x + toint - toint - x;
 	if (y > 0)
 		y -= 1;
 	x += y;