Fix strtold on 32-bit sparc (and probably others) (BZ #16965)

This patch fixes an issue observed running the tst-strtod-round test on
32 bit sparc. In some conditions, strtold calls round_and_return, which in
turn calls __mpn_rshift with cnt = 0, while stdlib/rshift.c explicitly says
that cnts should satisfy 0 < CNT < BITS_PER_MP_LIMB. In this case, the code
end up doing a logical shift right of the same amount than the register,
which is undefined in the C standard.

Due to this bug, 32-bit sparc does not correctly convert the value
"0x1p-16446", but it is likely that other architectures are also
affected for other input values.

diff --git a/ChangeLog b/ChangeLog
index 59464a6..e87fc22 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -11,6 +11,10 @@
        * localedata/tst-langinfo.sh: Send output to stdout.
        * localedata/tst-langinfo-static.c: New file.
 
+       [BZ #16965]
+       * stdlib/strtod_l.c (round_and_return): Add code to shift limbs
+       when the shift amount is modulo the limb size.
+
 2014-05-20  Richard Henderson  <rth@redhat.com>
 
        [BZ #16967]

diff --git a/NEWS b/NEWS
index d9ce8f9..8aaf2f4 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -18,7 +18,7 @@ Version 2.20
   16760, 16770, 16786, 16789, 16791, 16799, 16800, 16815, 16823, 16824,
   16831, 16838, 16849, 16854, 16876, 16877, 16885, 16888, 16890, 16912,
   16915, 16916, 16917, 16922, 16927, 16928, 16932, 16943, 16958, 16966,
-  16967.
+  16967, 16965.
 
 * The minimum Linux kernel version that this version of the GNU C Library
   can be used with is 2.6.32.

diff --git a/stdlib/strtod_l.c b/stdlib/strtod_l.c
index 6707e48..3c449c7 100644 (file)
--- a/stdlib/strtod_l.c
+++ b/stdlib/strtod_l.c
@@ -243,9 +243,14 @@ round_and_return (mp_limb_t *retval, intmax_t exponent, int negative,
          more_bits |= ((round_limb & ((((mp_limb_t) 1) << round_bit) - 1))
                        != 0);
 
-         (void) __mpn_rshift (retval, &retval[shift / BITS_PER_MP_LIMB],
-                              RETURN_LIMB_SIZE - (shift / BITS_PER_MP_LIMB),
-                              shift % BITS_PER_MP_LIMB);
+         /* __mpn_rshift requires 0 < shift < BITS_PER_MP_LIMB.  */
+         if ((shift % BITS_PER_MP_LIMB) != 0)
+           (void) __mpn_rshift (retval, &retval[shift / BITS_PER_MP_LIMB],
+                                RETURN_LIMB_SIZE - (shift / BITS_PER_MP_LIMB),
+                                shift % BITS_PER_MP_LIMB);
+         else
+           for (i = 0; i < RETURN_LIMB_SIZE - (shift / BITS_PER_MP_LIMB); i++)
+             retval[i] = retval[i + (shift / BITS_PER_MP_LIMB)];
          MPN_ZERO (&retval[RETURN_LIMB_SIZE - (shift / BITS_PER_MP_LIMB)],
                    shift / BITS_PER_MP_LIMB);
        }