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c++: Avoid UB in signed shift [PR 98625]

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I'd forgotten that left shifting a negative value is UB until C++20.
Insert some casts to do unsigned shifts.

	PT c++/98625
	gcc/cp/
	* module.cc (bytes_in::i, bytes_in::wi): Avoid left shift of
	signed type.
This commit is contained in:
Nathan Sidwell 2021-01-20 09:21:02 -08:00
parent e140f5fd3e
commit 911f797a9b
1 changed files with 8 additions and 2 deletions
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10
gcc/cp/module.cc
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@ -878,9 +878,12 @@ bytes_in::i ()
v &= 0xf;
if (v & 0x8)
v |= -1 ^ 0x7;
/* unsigned necessary due to left shifts of -ve values. */
unsigned uv = unsigned (v);
if ((ptr = read (++bytes)))
while (bytes--)
v = (v << 8) | (*ptr++ & 0xff);
uv = (uv << 8) | (*ptr++ & 0xff);
v = int (uv);
}
else if (v & 0x40)
v |= -1 ^ 0x3f;
@ -969,9 +972,12 @@ bytes_in::wi ()
v &= 0xf;
if (v & 0x8)
v |= -1 ^ 0x7;
/* unsigned necessary due to left shifts of -ve values. */
unsigned HOST_WIDE_INT uv = (unsigned HOST_WIDE_INT) v;
if ((ptr = read (++bytes)))
while (bytes--)
v = (v << 8) | (*ptr++ & 0xff);
uv = (uv << 8) | (*ptr++ & 0xff);
v = (HOST_WIDE_INT) uv;
}
else if (v & 0x40)
v |= -1 ^ 0x3f;