On Wed, Nov 09, 2011 at 09:35:51AM +0100, Stefan Farfeleder wrote:
> On Tue, Nov 08, 2011 at 11:54:39PM +0000, Jilles Tjoelker wrote:
> > Author: jilles
> > Date: Tue Nov 8 23:54:39 2011
> > New Revision: 227369
> > URL: http://svn.freebsd.org/changeset/base/227369
> > Log:
> > sh: Remove undefined behaviour due to overflow in +/-/* in arithmetic.
> > With i386 base gcc and i386 base clang, arith_yacc.o remains unchanged.
> > Modified:
> > head/bin/sh/arith_yacc.c
> > Modified: head/bin/sh/arith_yacc.c
> > ==============================================================================
> > --- head/bin/sh/arith_yacc.c Tue Nov 8 23:44:26 2011
> > (r227368)
> > +++ head/bin/sh/arith_yacc.c Tue Nov 8 23:54:39 2011
> > (r227369)
> > @@ -131,11 +131,11 @@ static arith_t do_binop(int op, arith_t
> > yyerror("divide error");
> > return op == ARITH_REM ? a % b : a / b;
> > case ARITH_MUL:
> > - return a * b;
> > + return (uintmax_t)a * (uintmax_t)b;
> > case ARITH_ADD:
> > - return a + b;
> > + return (uintmax_t)a + (uintmax_t)b;
> > case ARITH_SUB:
> > - return a - b;
> > + return (uintmax_t)a - (uintmax_t)b;
> > case ARITH_LSHIFT:
> > return a << b;
> > case ARITH_RSHIFT:
> Isn't the behaviour undefined too when you convert an out-of-range
> uintmax_t value back into an intmax_t value?
The result is implementation-defined or an implementation-defined signal
is raised.
GCC documentation (gcc.info 4.5 Integers implementation) says this
] * `The result of, or the signal raised by, converting an integer to a
] signed integer type when the value cannot be represented in an
] object of that type (C90 6.2.1.2, C99 6.3.1.3).'
] For conversion to a type of width N, the value is reduced modulo
] 2^N to be within range of the type; no signal is raised.
which is exactly what we need.
--
Jilles Tjoelker
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