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authorDenys Vlasenko <vda.linux@googlemail.com>2010-10-30 21:45:41 (GMT)
committerDenys Vlasenko <vda.linux@googlemail.com>2010-10-30 21:45:41 (GMT)
commit4435b3ae24b6f76892b7c06c300687c23fab2729 (patch)
tree7fd9676b25e7177963eca799831497354fe1b5ae /libm
parentae73aafe99fa6bb5e7422f2bdedea39f03ead72c (diff)
libm: fix rint/scalb testcase failures
These failures no longer happen: Failure: Test: scalb (2.0, 0.5) == NaN plus invalid exception Failure: Test: scalb (3.0, -2.5) == NaN plus invalid exception Failure: Test: rint (0.5) == 0.0 Failure: Test: rint (1.5) == 2.0 Failure: Test: rint (2.5) == 2.0 Failure: Test: rint (3.5) == 4.0 Failure: Test: rint (4.5) == 4.0 Failure: Test: rint (-0.5) == -0.0 Failure: Test: rint (-1.5) == -2.0 Failure: Test: rint (-2.5) == -2.0 Failure: Test: rint (-3.5) == -4.0 Failure: Test: rint (-4.5) == -4.0 Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'libm')
-rw-r--r--libm/s_rint.c54
1 files changed, 35 insertions, 19 deletions
diff --git a/libm/s_rint.c b/libm/s_rint.c
index 358ce76..06432c6 100644
--- a/libm/s_rint.c
+++ b/libm/s_rint.c
@@ -30,41 +30,57 @@ TWO52[2]={
double rint(double x)
{
- int32_t i0,j0,sx;
+ int32_t i0, j0, sx;
u_int32_t i,i1;
- double w,t;
+ double t;
+ /* We use w = x + 2^52; t = w - 2^52; trick to round x to integer.
+ * This trick requires that compiler does not optimize it
+ * by keeping intermediate result w in a register wider than double.
+ * Declaring w volatile assures that value gets truncated to double
+ * (unfortunately, it also forces store+load):
+ */
+ volatile double w;
+
EXTRACT_WORDS(i0,i1,x);
- sx = (i0>>31)&1;
- j0 = ((i0>>20)&0x7ff)-0x3ff;
- if(j0<20) {
- if(j0<0) {
- if(((i0&0x7fffffff)|i1)==0) return x;
+ /* Unbiased exponent */
+ j0 = ((((u_int32_t)i0) >> 20)&0x7ff)-0x3ff;
+
+ if (j0 > 51) {
+ //Why bother? Just returning x works too
+ //if (j0 == 0x400) /* inf or NaN */
+ // return x+x;
+ return x; /* x is integral */
+ }
+
+ /* Sign */
+ sx = ((u_int32_t)i0) >> 31;
+
+ if (j0<20) {
+ if (j0<0) { /* |x| < 1 */
+ if (((i0&0x7fffffff)|i1)==0) return x;
i1 |= (i0&0x0fffff);
i0 &= 0xfffe0000;
i0 |= ((i1|-i1)>>12)&0x80000;
SET_HIGH_WORD(x,i0);
- w = TWO52[sx]+x;
- t = w-TWO52[sx];
+ w = TWO52[sx]+x;
+ t = w-TWO52[sx];
GET_HIGH_WORD(i0,t);
SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
- return t;
+ return t;
} else {
i = (0x000fffff)>>j0;
- if(((i0&i)|i1)==0) return x; /* x is integral */
+ if (((i0&i)|i1)==0) return x; /* x is integral */
i>>=1;
- if(((i0&i)|i1)!=0) {
- if(j0==19) i1 = 0x40000000; else
- i0 = (i0&(~i))|((0x20000)>>j0);
+ if (((i0&i)|i1)!=0) {
+ if (j0==19) i1 = 0x40000000;
+ else i0 = (i0&(~i))|((0x20000)>>j0);
}
}
- } else if (j0>51) {
- if(j0==0x400) return x+x; /* inf or NaN */
- else return x; /* x is integral */
} else {
i = ((u_int32_t)(0xffffffff))>>(j0-20);
- if((i1&i)==0) return x; /* x is integral */
+ if ((i1&i)==0) return x; /* x is integral */
i>>=1;
- if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
+ if ((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
}
INSERT_WORDS(x,i0,i1);
w = TWO52[sx]+x;