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Patch to fix lshift_double and rshift_double prec handling
- To: gcc-patches at gcc dot gnu dot org
- Subject: Patch to fix lshift_double and rshift_double prec handling
- From: John Wehle <john at feith dot com>
- Date: Thu, 8 Nov 2001 11:38:16 -0500 (EST)
The lshift_double and rshift_double PREC argument is documented as
controlling the number of bits in the result. Unfortunately they
don't actually contain any code to implement this.
Consider using rshift_double to perform a logical shift right of
QImode -4.
l1 h1 count prec *lv *hv
0xfffffffc 0xffffffff 1 8 produces 0xfffffffe 0x7fffffff
instead of 0x0000007e 0x00000000
Or using rrotate_double (which uses rshift_double) to rotate QImode -4:
0xfffffffc 0xffffffff 1 8 produces 0xfffffffe 0xffffffff
instead of 0x0000007e 0x00000000
simplify_binary_operation, lrotate_double, and rrotate_double all seem
to expect PREC to be honored (which it currently isn't).
This patch passes make bootstrap and make check on Dec Alpha 4.0f
and Solaris 7 x86.
ChangeLog:
Wed Nov 7 16:20:32 EST 2001 John Wehle (john@feith.com)
* fold-const.c (lshift_double): Honor PREC.
(rshift_double): Likewise.
Enjoy!
-- John Wehle
------------------8<------------------------8<------------------------
*** gcc/fold-const.c.ORIGINAL Wed Nov 7 12:00:14 2001
--- gcc/fold-const.c Wed Nov 7 16:59:42 2001
*************** lshift_double (l1, h1, count, prec, lv,
*** 383,388 ****
--- 383,390 ----
HOST_WIDE_INT *hv;
int arith;
{
+ unsigned HOST_WIDE_INT signmask;
+
if (count < 0)
{
rshift_double (l1, h1, -count, prec, lv, hv, arith);
*************** lshift_double (l1, h1, count, prec, lv,
*** 412,417 ****
--- 414,439 ----
| (l1 >> (HOST_BITS_PER_WIDE_INT - count - 1) >> 1));
*lv = l1 << count;
}
+
+ /* Sign extend all bits that are beyond the precision. */
+
+ signmask = -((prec > HOST_BITS_PER_WIDE_INT
+ ? (*hv >> (prec - HOST_BITS_PER_WIDE_INT - 1))
+ : (*lv >> (prec - 1))) & 1);
+
+ if (prec >= 2 * HOST_BITS_PER_WIDE_INT)
+ ;
+ else if (prec >= HOST_BITS_PER_WIDE_INT)
+ {
+ *hv &= ~((HOST_WIDE_INT) (-1) << (prec - HOST_BITS_PER_WIDE_INT));
+ *hv |= signmask << (prec - HOST_BITS_PER_WIDE_INT);
+ }
+ else
+ {
+ *hv = signmask;
+ *lv &= ~((unsigned HOST_WIDE_INT) (-1) << prec);
+ *lv |= signmask << prec;
+ }
}
/* Shift the doubleword integer in L1, H1 right by COUNT places
*************** void
*** 423,429 ****
rshift_double (l1, h1, count, prec, lv, hv, arith)
unsigned HOST_WIDE_INT l1;
HOST_WIDE_INT h1, count;
! unsigned int prec ATTRIBUTE_UNUSED;
unsigned HOST_WIDE_INT *lv;
HOST_WIDE_INT *hv;
int arith;
--- 445,451 ----
rshift_double (l1, h1, count, prec, lv, hv, arith)
unsigned HOST_WIDE_INT l1;
HOST_WIDE_INT h1, count;
! unsigned int prec;
unsigned HOST_WIDE_INT *lv;
HOST_WIDE_INT *hv;
int arith;
*************** rshift_double (l1, h1, count, prec, lv,
*** 443,463 ****
{
/* Shifting by the host word size is undefined according to the
ANSI standard, so we must handle this as a special case. */
! *hv = signmask;
! *lv = signmask;
}
else if (count >= HOST_BITS_PER_WIDE_INT)
{
! *hv = signmask;
! *lv = ((signmask << (2 * HOST_BITS_PER_WIDE_INT - count - 1) << 1)
! | ((unsigned HOST_WIDE_INT) h1 >> (count - HOST_BITS_PER_WIDE_INT)));
}
else
{
*lv = ((l1 >> count)
| ((unsigned HOST_WIDE_INT) h1 << (HOST_BITS_PER_WIDE_INT - count - 1) << 1));
! *hv = ((signmask << (HOST_BITS_PER_WIDE_INT - count))
! | ((unsigned HOST_WIDE_INT) h1 >> count));
}
}
--- 465,504 ----
{
/* Shifting by the host word size is undefined according to the
ANSI standard, so we must handle this as a special case. */
! *hv = 0;
! *lv = 0;
}
else if (count >= HOST_BITS_PER_WIDE_INT)
{
! *hv = 0;
! *lv = (unsigned HOST_WIDE_INT) h1 >> (count - HOST_BITS_PER_WIDE_INT);
}
else
{
+ *hv = (unsigned HOST_WIDE_INT) h1 >> count;
*lv = ((l1 >> count)
| ((unsigned HOST_WIDE_INT) h1 << (HOST_BITS_PER_WIDE_INT - count - 1) << 1));
! }
!
! /* Zero / sign extend all bits that are beyond the precision. */
!
! if (count >= (HOST_WIDE_INT)prec)
! {
! *hv = signmask;
! *lv = signmask;
! }
! else if ((prec - count) >= 2 * HOST_BITS_PER_WIDE_INT)
! ;
! else if ((prec - count) >= HOST_BITS_PER_WIDE_INT)
! {
! *hv &= ~((HOST_WIDE_INT) (-1) << (prec - count - HOST_BITS_PER_WIDE_INT));
! *hv |= signmask << (prec - count - HOST_BITS_PER_WIDE_INT);
! }
! else
! {
! *hv = signmask;
! *lv &= ~((unsigned HOST_WIDE_INT) (-1) << (prec - count));
! *lv |= signmask << (prec - count);
}
}
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