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Do not raise "inexact" from generic floor (bug 15479) [committed]


C99 and C11 allow but do not require ceil, floor, round and trunc to
raise the "inexact" exception for noninteger arguments.  TS 18661-1
requires that this exception not be raised by these functions.  This
aligns them with general IEEE semantics, where "inexact" is only
raised if the final step of rounding the infinite-precision result to
the result type is inexact; for these functions, the
infinite-precision integer result is always representable in the
result type, so "inexact" should never be raised.

The generic implementations of ceil, floor and round functions contain
code to force "inexact" to be raised.  This patch removes it for floor
functions to align them with TS 18661-1 in this regard.  Note that
some architecture-specific versions may still raise "inexact", so the
tests are not updated and the bug is not yet fixed.

Tested for x86_64, x86 and mips64.  Committed.

2016-05-24  Joseph Myers  <joseph@codesourcery.com>

	[BZ #15479]
	* sysdeps/ieee754/dbl-64/s_floor.c: Do not mention "inexact"
	exception in comment.
	(huge): Remove variable.
	(__floor): Do not force "inexact" exception.
	* sysdeps/ieee754/dbl-64/wordsize-64/s_floor.c: Do not mention
	"inexact" exception in comment.
	(huge): Remove variable.
	(__floor): Do not force "inexact" exception.
	* sysdeps/ieee754/flt-32/s_floorf.c: Do not mention "inexact"
	exception in comment.
	(huge): Remove variable.
	(__floorf): Do not force "inexact" exception.
	* sysdeps/ieee754/ldbl-128/s_floorl.c: Do not mention "inexact"
	exception in comment.
	(huge): Remove variable.
	(__floorl): Do not force "inexact" exception.

diff --git a/sysdeps/ieee754/dbl-64/s_floor.c b/sysdeps/ieee754/dbl-64/s_floor.c
index bd6afa7..8f86aa3 100644
--- a/sysdeps/ieee754/dbl-64/s_floor.c
+++ b/sysdeps/ieee754/dbl-64/s_floor.c
@@ -15,15 +15,11 @@
  * Return x rounded toward -inf to integral value
  * Method:
  *	Bit twiddling.
- * Exception:
- *	Inexact flag raised if x not equal to floor(x).
  */
 
 #include <math.h>
 #include <math_private.h>
 
-static const double huge = 1.0e300;
-
 double
 __floor (double x)
 {
@@ -33,9 +29,9 @@ __floor (double x)
   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
   if (j0 < 20)
     {
-      if (j0 < 0)       /* raise inexact if x != 0 */
+      if (j0 < 0)
 	{
-	  math_force_eval (huge + x);   /* return 0*sign(x) if |x|<1 */
+	  /* return 0*sign(x) if |x|<1 */
 	  if (i0 >= 0)
 	    {
 	      i0 = i1 = 0;
@@ -50,7 +46,6 @@ __floor (double x)
 	  i = (0x000fffff) >> j0;
 	  if (((i0 & i) | i1) == 0)
 	    return x;                        /* x is integral */
-	  math_force_eval (huge + x);           /* raise inexact flag */
 	  if (i0 < 0)
 	    i0 += (0x00100000) >> j0;
 	  i0 &= (~i); i1 = 0;
@@ -68,7 +63,6 @@ __floor (double x)
       i = ((u_int32_t) (0xffffffff)) >> (j0 - 20);
       if ((i1 & i) == 0)
 	return x;                       /* x is integral */
-      math_force_eval (huge + x);               /* raise inexact flag */
       if (i0 < 0)
 	{
 	  if (j0 == 20)
diff --git a/sysdeps/ieee754/dbl-64/wordsize-64/s_floor.c b/sysdeps/ieee754/dbl-64/wordsize-64/s_floor.c
index b7ed14b..8d514f2 100644
--- a/sysdeps/ieee754/dbl-64/wordsize-64/s_floor.c
+++ b/sysdeps/ieee754/dbl-64/wordsize-64/s_floor.c
@@ -39,12 +39,8 @@
  * Return x rounded toward -inf to integral value
  * Method:
  *	Bit twiddling.
- * Exception:
- *	Inexact flag raised if x not equal to floor(x).
  */
 
-static const double huge = 1.0e300;
-
 
 double
 __floor (double x)
@@ -53,15 +49,14 @@ __floor (double x)
 	EXTRACT_WORDS64(i0,x);
 	int32_t j0 = ((i0>>52)&0x7ff)-0x3ff;
 	if(__builtin_expect(j0<52, 1)) {
-	    if(j0<0) {	/* raise inexact if x != 0 */
-		math_force_eval(huge+x);/* return 0*sign(x) if |x|<1 */
+	    if(j0<0) {
+		/* return 0*sign(x) if |x|<1 */
 		if(i0>=0) {i0=0;}
 		else if((i0&0x7fffffffffffffffl)!=0)
 		  { i0=0xbff0000000000000l;}
 	    } else {
 		uint64_t i = (0x000fffffffffffffl)>>j0;
 		if((i0&i)==0) return x; /* x is integral */
-		math_force_eval(huge+x);	/* raise inexact flag */
 		if(i0<0) i0 += (0x0010000000000000l)>>j0;
 		i0 &= (~i);
 	    }
diff --git a/sysdeps/ieee754/flt-32/s_floorf.c b/sysdeps/ieee754/flt-32/s_floorf.c
index 99d6c01..69160e5 100644
--- a/sysdeps/ieee754/flt-32/s_floorf.c
+++ b/sysdeps/ieee754/flt-32/s_floorf.c
@@ -18,15 +18,11 @@
  * Return x rounded toward -inf to integral value
  * Method:
  *	Bit twiddling.
- * Exception:
- *	Inexact flag raised if x not equal to floorf(x).
  */
 
 #include <math.h>
 #include <math_private.h>
 
-static const float huge = 1.0e30;
-
 float
 __floorf(float x)
 {
@@ -35,15 +31,14 @@ __floorf(float x)
 	GET_FLOAT_WORD(i0,x);
 	j0 = ((i0>>23)&0xff)-0x7f;
 	if(j0<23) {
-	    if(j0<0) {	/* raise inexact if x != 0 */
-		math_force_eval(huge+x);/* return 0*sign(x) if |x|<1 */
+	    if(j0<0) {
+		/* return 0*sign(x) if |x|<1 */
 		if(i0>=0) {i0=0;}
 		else if((i0&0x7fffffff)!=0)
 		  { i0=0xbf800000;}
 	    } else {
 		i = (0x007fffff)>>j0;
 		if((i0&i)==0) return x; /* x is integral */
-		math_force_eval(huge+x);	/* raise inexact flag */
 		if(i0<0) i0 += (0x00800000)>>j0;
 		i0 &= (~i);
 	    }
diff --git a/sysdeps/ieee754/ldbl-128/s_floorl.c b/sysdeps/ieee754/ldbl-128/s_floorl.c
index c72d5d4..14a0efe 100644
--- a/sysdeps/ieee754/ldbl-128/s_floorl.c
+++ b/sysdeps/ieee754/ldbl-128/s_floorl.c
@@ -22,15 +22,11 @@ static char rcsid[] = "$NetBSD: $";
  * Return x rounded toward -inf to integral value
  * Method:
  *	Bit twiddling.
- * Exception:
- *	Inexact flag raised if x not equal to floor(x).
  */
 
 #include <math.h>
 #include <math_private.h>
 
-static const long double huge = 1.0e4930L;
-
 long double __floorl(long double x)
 {
 	int64_t i0,i1,j0;
@@ -38,19 +34,16 @@ long double __floorl(long double x)
 	GET_LDOUBLE_WORDS64(i0,i1,x);
 	j0 = ((i0>>48)&0x7fff)-0x3fff;
 	if(j0<48) {
-	    if(j0<0) { 	/* raise inexact if x != 0 */
-		if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
-		    if(i0>=0) {i0=i1=0;}
-		    else if(((i0&0x7fffffffffffffffLL)|i1)!=0)
-			{ i0=0xbfff000000000000ULL;i1=0;}
-		}
+	    if(j0<0) {
+		/* return 0*sign(x) if |x|<1 */
+		if(i0>=0) {i0=i1=0;}
+		else if(((i0&0x7fffffffffffffffLL)|i1)!=0)
+		    { i0=0xbfff000000000000ULL;i1=0;}
 	    } else {
 		i = (0x0000ffffffffffffULL)>>j0;
 		if(((i0&i)|i1)==0) return x; /* x is integral */
-		if(huge+x>0.0) {	/* raise inexact flag */
-		    if(i0<0) i0 += (0x0001000000000000LL)>>j0;
-		    i0 &= (~i); i1=0;
-		}
+		if(i0<0) i0 += (0x0001000000000000LL)>>j0;
+		i0 &= (~i); i1=0;
 	    }
 	} else if (j0>111) {
 	    if(j0==0x4000) return x+x;	/* inf or NaN */
@@ -58,17 +51,15 @@ long double __floorl(long double x)
 	} else {
 	    i = -1ULL>>(j0-48);
 	    if((i1&i)==0) return x;	/* x is integral */
-	    if(huge+x>0.0) { 		/* raise inexact flag */
-		if(i0<0) {
-		    if(j0==48) i0+=1;
-		    else {
-			j = i1+(1LL<<(112-j0));
-			if(j<i1) i0 +=1 ; 	/* got a carry */
-			i1=j;
-		    }
+	    if(i0<0) {
+		if(j0==48) i0+=1;
+		else {
+		    j = i1+(1LL<<(112-j0));
+		    if(j<i1) i0 +=1 ; 	/* got a carry */
+		    i1=j;
 		}
-		i1 &= (~i);
 	    }
+	    i1 &= (~i);
 	}
 	SET_LDOUBLE_WORDS64(x,i0,i1);
 	return x;

-- 
Joseph S. Myers
joseph@codesourcery.com


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