On 22/07/18 21:31, Ramsay Jones wrote: > > > On 22/07/18 21:26, Ramsay Jones wrote: > [snip] >>> +* shift instructions: >>> + the type of the result must be the same as the type >>> + of the left operand but the type of the right operand >>> + is independent. >> >> But for constant shifts, the shift direction can be flipped >> and the shift amount made non-negative, right? > > Hmm, except that is not allowed by the C standard? (need to > check). Yep, C11, 6.5.7-3 says: 3 The integer promotions are performed on each of the operands. The type of the result is that of the promoted left operand. If the value of the right operand is negative or is greater than or equal to the width of the promoted left operand, the behavior is undefined. ... and a few experiments with gcc seems to indicate that negative shifts (left or right) return zero. ATB, Ramsay Jones -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
