Hi Paolo,
On 5/12/21 11:54 AM, Paolo Bonzini wrote:
> Avoid possible uninitialized variables on machines where
> division by zero does not trap. Add __divmoddi4, and
> use it in __moddi3 and __divdi3.
Looks good now, I like the change to __moddi3 and __divdi3 as that means that the
tests will cover __divmoddi4, and the functions are now similar to their unsigned
counterparts:
Reviewed-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
Thanks,
Alex
>
> Reported-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> lib/ldiv32.c | 40 ++++++++++++++++++++++++----------------
> 1 file changed, 24 insertions(+), 16 deletions(-)
>
> diff --git a/lib/ldiv32.c b/lib/ldiv32.c
> index 96f4b35..897a4b9 100644
> --- a/lib/ldiv32.c
> +++ b/lib/ldiv32.c
> @@ -1,6 +1,7 @@
> #include <stdint.h>
>
> extern uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem);
> +extern int64_t __divmoddi4(int64_t num, int64_t den, int64_t *p_rem);
> extern int64_t __moddi3(int64_t num, int64_t den);
> extern int64_t __divdi3(int64_t num, int64_t den);
> extern uint64_t __udivdi3(uint64_t num, uint64_t den);
> @@ -11,8 +12,11 @@ uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem)
> uint64_t quot = 0;
>
> /* Trigger a division by zero at run time (trick taken from iPXE). */
> - if (den == 0)
> + if (den == 0) {
> + if (p_rem)
> + *p_rem = 0;
> return 1/((unsigned)den);
> + }
>
> if (num >= den) {
> /* Align den to num to avoid wasting time on leftmost zero bits. */
> @@ -35,31 +39,35 @@ uint64_t __udivmoddi4(uint64_t num, uint64_t den, uint64_t *p_rem)
> return quot;
> }
>
> -int64_t __moddi3(int64_t num, int64_t den)
> +int64_t __divmoddi4(int64_t num, int64_t den, int64_t *p_rem)
> {
> - uint64_t mask = num < 0 ? -1 : 0;
> + int32_t nmask = num < 0 ? -1 : 0;
> + int32_t qmask = (num ^ den) < 0 ? -1 : 0;
> + uint64_t quot;
>
> /* Compute absolute values and do an unsigned division. */
> - num = (num + mask) ^ mask;
> + num = (num + nmask) ^ nmask;
> if (den < 0)
> den = -den;
>
> - /* Copy sign of num into result. */
> - return (__umoddi3(num, den) + mask) ^ mask;
> + /* Copy sign of num^den into quotient, sign of num into remainder. */
> + quot = (__udivmoddi4(num, den, (uint64_t *)p_rem) + qmask) ^ qmask;
> + if (p_rem)
> + *p_rem = (*p_rem + nmask) ^ nmask;
> + return quot;
> }
>
> -int64_t __divdi3(int64_t num, int64_t den)
> +int64_t __moddi3(int64_t num, int64_t den)
> {
> - uint64_t mask = (num ^ den) < 0 ? -1 : 0;
> -
> - /* Compute absolute values and do an unsigned division. */
> - if (num < 0)
> - num = -num;
> - if (den < 0)
> - den = -den;
> + int64_t rem;
> + __divmoddi4(num, den, &rem);
> + return rem;
> +}
>
> - /* Copy sign of num^den into result. */
> - return (__udivdi3(num, den) + mask) ^ mask;
> +int64_t __divdi3(int64_t num, int64_t den)
> +{
> + int64_t rem;
> + return __divmoddi4(num, den, &rem);
> }
>
> uint64_t __udivdi3(uint64_t num, uint64_t den)
