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* libm/common/fdlibm.h (SAFE_LEFT_SHIFT): New macro definition.

Browse Source 
(SAFE_RIGHT_SHIFT): Likewise.
	* libm/common/s_llround.c (llround): Annotate shift operations with
	possible shift amount ranges, and use SAFE_RIGHT_SHIFT to avoid
	undefined behaviour.
	* libm/common/s_lround.c (lround): Likewise.
This commit is contained in:
Dave Korn 2010-07-20 01:33:05 +00:00
parent 2af268382a
commit e561d3e77e
4 changed files with 62 additions and 7 deletions
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9
newlib/ChangeLog
View File

@ -1,3 +1,12 @@
2010-07-20 Dave Korn <dave.korn.cygwin@gmail.com>
* libm/common/fdlibm.h (SAFE_LEFT_SHIFT): New macro definition.
(SAFE_RIGHT_SHIFT): Likewise.
* libm/common/s_llround.c (llround): Annotate shift operations with
possible shift amount ranges, and use SAFE_RIGHT_SHIFT to avoid
undefined behaviour.
* libm/common/s_lround.c (lround): Likewise.
2010-07-19 Eric Blake <eblake@redhat.com>
* libc/stdio/mktemp.c (_gettemp): Add parameter, all callers

10
newlib/libm/common/fdlibm.h
View File

@ -361,3 +361,13 @@ do { \
sf_u.word = (i); \
(d) = sf_u.value; \
} while (0)
/* Macros to avoid undefined behaviour that can arise if the amount
of a shift is exactly equal to the size of the shifted operand. */
#define SAFE_LEFT_SHIFT(op,amt) \
(((amt) < 8 * sizeof(op)) ? ((op) << (amt)) : 0)
#define SAFE_RIGHT_SHIFT(op,amt) \
(((amt) < 8 * sizeof(op)) ? ((op) >> (amt)) : 0)

22
newlib/libm/common/s_llround.c
View File

@ -31,8 +31,10 @@ llround(double x)
msw &= 0x000fffff;
msw |= 0x00100000;
/* exponent_less_1023 in [-1024,1023] */
if (exponent_less_1023 < 20)
{
/* exponent_less_1023 in [-1024,19] */
if (exponent_less_1023 < 0)
{
if (exponent_less_1023 < -1)
@ -42,20 +44,34 @@ llround(double x)
}
else
{
/* exponent_less_1023 in [0,19] */
/* shift amt in [0,19] */
msw += 0x80000 >> exponent_less_1023;
/* shift amt in [20,1] */
result = msw >> (20 - exponent_less_1023);
}
}
else if (exponent_less_1023 < (8 * sizeof (long long int)) - 1)
{
/* 64bit longlong: exponent_less_1023 in [20,62] */
if (exponent_less_1023 >= 52)
result = ((long long int) msw << (exponent_less_1023 - 20)) | (lsw << (exponent_less_1023 - 52));
/* 64bit longlong: exponent_less_1023 in [52,62] */
/* 64bit longlong: shift amt in [32,42] */
result = ((long long int) msw << (exponent_less_1023 - 20))
/* 64bit longlong: shift amt in [0,10] */
| (lsw << (exponent_less_1023 - 52));
else
{
unsigned int tmp = lsw + (0x80000000 >> (exponent_less_1023 - 20));
/* 64bit longlong: exponent_less_1023 in [20,51] */
unsigned int tmp = lsw
/* 64bit longlong: shift amt in [0,31] */
+ (0x80000000 >> (exponent_less_1023 - 20));
if (tmp < lsw)
++msw;
result = ((long long int) msw << (exponent_less_1023 - 20)) | (tmp >> (52 - exponent_less_1023));
/* 64bit longlong: shift amt in [0,31] */
result = ((long long int) msw << (exponent_less_1023 - 20))
/* ***64bit longlong: shift amt in [32,1] */
| SAFE_RIGHT_SHIFT (tmp, (52 - exponent_less_1023));
}
}
else

28
newlib/libm/common/s_lround.c
View File

@ -71,9 +71,10 @@ ANSI C, POSIX
exponent_less_1023 = ((msw & 0x7ff00000) >> 20) - 1023;
msw &= 0x000fffff;
msw |= 0x00100000;
/* exponent_less_1023 in [-1024,1023] */
if (exponent_less_1023 < 20)
{
/* exponent_less_1023 in [-1024,19] */
if (exponent_less_1023 < 0)
{
if (exponent_less_1023 < -1)
@ -83,20 +84,39 @@ ANSI C, POSIX
}
else
{
/* exponent_less_1023 in [0,19] */
/* shift amt in [0,19] */
msw += 0x80000 >> exponent_less_1023;
/* shift amt in [20,1] */
result = msw >> (20 - exponent_less_1023);
}
}
else if (exponent_less_1023 < (8 * sizeof (long int)) - 1)
{
/* 32bit long: exponent_less_1023 in [20,30] */
/* 64bit long: exponent_less_1023 in [20,62] */
if (exponent_less_1023 >= 52)
result = ((long int) msw << (exponent_less_1023 - 20)) | (lsw << (exponent_less_1023 - 52));
/* 64bit long: exponent_less_1023 in [52,62] */
/* 64bit long: shift amt in [32,42] */
result = ((long int) msw << (exponent_less_1023 - 20))
/* 64bit long: shift amt in [0,10] */
| (lsw << (exponent_less_1023 - 52));
else
{
unsigned int tmp = lsw + (0x80000000 >> (exponent_less_1023 - 20));
/* 32bit long: exponent_less_1023 in [20,30] */
/* 64bit long: exponent_less_1023 in [20,51] */
unsigned int tmp = lsw
/* 32bit long: shift amt in [0,10] */
/* 64bit long: shift amt in [0,31] */
+ (0x80000000 >> (exponent_less_1023 - 20));
if (tmp < lsw)
++msw;
result = ((long int) msw << (exponent_less_1023 - 20)) | (tmp >> (52 - exponent_less_1023));
/* 32bit long: shift amt in [0,10] */
/* 64bit long: shift amt in [0,31] */
result = ((long int) msw << (exponent_less_1023 - 20))
/* ***32bit long: shift amt in [32,22] */
/* ***64bit long: shift amt in [32,1] */
| SAFE_RIGHT_SHIFT (tmp, (52 - exponent_less_1023));
}
}
else