Hi!
The big-endian _BitInt support in libgcc was written without any
testing and so I haven't discovered I've made one mistake in it
(in multiple places).
The bitint_reduce_prec function attempts to optimize inputs
which have some larger precision but at runtime they are found
to need smaller number of limbs.
For little-endian that is handled just by returning smaller
precision (or negative precision for signed), but for
big-endian we need to adjust the passed in limb pointer so that
when it returns smaller precision the argument still contains
the least significant limbs for the returned precision.
Bootstrapped/regtested on x86_64-linux and i686-linux (where it
doesn't do anything) and tested with all the _BitInt related
tests on s390x-linux, ok for trunk?
2025-05-19 Jakub Jelinek <ja...@redhat.com>
* libgcc2.c (bitint_reduce_prec): For big endian
__LIBGCC_BITINT_ORDER__ use ++*p and --*p instead of
++p and --p.
* soft-fp/bitint.h (bitint_reduce_prec): Likewise.
--- libgcc/libgcc2.c.jj 2025-04-08 14:09:53.632413447 +0200
+++ libgcc/libgcc2.c 2025-05-14 17:16:48.642879943 +0200
@@ -1333,7 +1333,7 @@ bitint_reduce_prec (const UBILtype **p,
if (prec >= -1)
return -2;
#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__
- ++p;
+ ++*p;
#else
--i;
#endif
@@ -1347,7 +1347,7 @@ bitint_reduce_prec (const UBILtype **p,
if (prec >= -1)
return -2;
#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__
- ++p;
+ ++*p;
#else
--i;
#endif
@@ -1358,7 +1358,7 @@ bitint_reduce_prec (const UBILtype **p,
if ((Wtype) mslimb >= 0)
{
#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__
- --p;
+ --*p;
#endif
return prec - 1;
}
@@ -1387,7 +1387,7 @@ bitint_reduce_prec (const UBILtype **p,
if (prec == 0)
return 1;
#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__
- ++p;
+ ++*p;
#else
--i;
#endif
@@ -1400,7 +1400,7 @@ bitint_reduce_prec (const UBILtype **p,
if (prec == 0)
return 1;
#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__
- ++p;
+ ++*p;
#else
--i;
#endif
--- libgcc/soft-fp/bitint.h.jj 2024-02-13 10:32:57.730666010 +0100
+++ libgcc/soft-fp/bitint.h 2025-05-14 17:17:00.418723808 +0200
@@ -76,7 +76,7 @@ bitint_reduce_prec (const UBILtype **p,
if (prec >= -1)
return -2;
#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__
- ++p;
+ ++*p;
#else
--i;
#endif
@@ -90,7 +90,7 @@ bitint_reduce_prec (const UBILtype **p,
if (prec >= -1)
return -2;
#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__
- ++p;
+ ++*p;
#else
--i;
#endif
@@ -101,7 +101,7 @@ bitint_reduce_prec (const UBILtype **p,
if ((BILtype) mslimb >= 0)
{
#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__
- --p;
+ --*p;
#endif
return prec - 1;
}
@@ -130,7 +130,7 @@ bitint_reduce_prec (const UBILtype **p,
if (prec == 0)
return 1;
#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__
- ++p;
+ ++*p;
#else
--i;
#endif
@@ -143,7 +143,7 @@ bitint_reduce_prec (const UBILtype **p,
if (prec == 0)
return 1;
#if __LIBGCC_BITINT_ORDER__ == __ORDER_BIG_ENDIAN__
- ++p;
+ ++*p;
#else
--i;
#endif
Jakub
