On Mon, Apr 11, 2011 at 04:32:08PM +0100, Peter Maydell wrote:
> In the VABAL instruction we take the absolute difference of two
> values of size x and store it in a result of size 2x. This means
> we have to be careful to calculate the absolute difference using
> a wide enough type that we don't accidentally overflow.
>
> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
> ---
> target-arm/neon_helper.c | 38 +++++++++++++++++++++-----------------
> 1 files changed, 21 insertions(+), 17 deletions(-)
>
> diff --git a/target-arm/neon_helper.c b/target-arm/neon_helper.c
> index c3ac96a..7df925a 100644
> --- a/target-arm/neon_helper.c
> +++ b/target-arm/neon_helper.c
> @@ -1514,9 +1514,13 @@ uint64_t HELPER(neon_addl_saturate_s64)(uint64_t a,
> uint64_t b)
> return result;
> }
>
> -#define DO_ABD(dest, x, y, type) do { \
> - type tmp_x = x; \
> - type tmp_y = y; \
> +/* We have to do the arithmetic in a larger type than
> + * the input type, because for example with a signed 32 bit
> + * op the absolute difference can overflow a signed 32 bit value.
> + */
> +#define DO_ABD(dest, x, y, intype, arithtype) do { \
> + arithtype tmp_x = (intype)(x); \
> + arithtype tmp_y = (intype)(y); \
> dest = ((tmp_x > tmp_y) ? tmp_x - tmp_y : tmp_y - tmp_x); \
> } while(0)
>
> @@ -1524,12 +1528,12 @@ uint64_t HELPER(neon_abdl_u16)(uint32_t a, uint32_t b)
> {
> uint64_t tmp;
> uint64_t result;
> - DO_ABD(result, a, b, uint8_t);
> - DO_ABD(tmp, a >> 8, b >> 8, uint8_t);
> + DO_ABD(result, a, b, uint8_t, uint32_t);
> + DO_ABD(tmp, a >> 8, b >> 8, uint8_t, uint32_t);
> result |= tmp << 16;
> - DO_ABD(tmp, a >> 16, b >> 16, uint8_t);
> + DO_ABD(tmp, a >> 16, b >> 16, uint8_t, uint32_t);
> result |= tmp << 32;
> - DO_ABD(tmp, a >> 24, b >> 24, uint8_t);
> + DO_ABD(tmp, a >> 24, b >> 24, uint8_t, uint32_t);
> result |= tmp << 48;
> return result;
> }
Do we really need a 32-bit type for the computation here?
> @@ -1538,12 +1542,12 @@ uint64_t HELPER(neon_abdl_s16)(uint32_t a, uint32_t b)
> {
> uint64_t tmp;
> uint64_t result;
> - DO_ABD(result, a, b, int8_t);
> - DO_ABD(tmp, a >> 8, b >> 8, int8_t);
> + DO_ABD(result, a, b, int8_t, int32_t);
> + DO_ABD(tmp, a >> 8, b >> 8, int8_t, int32_t);
> result |= tmp << 16;
> - DO_ABD(tmp, a >> 16, b >> 16, int8_t);
> + DO_ABD(tmp, a >> 16, b >> 16, int8_t, int32_t);
> result |= tmp << 32;
> - DO_ABD(tmp, a >> 24, b >> 24, int8_t);
> + DO_ABD(tmp, a >> 24, b >> 24, int8_t, int32_t);
> result |= tmp << 48;
> return result;
> }
Ditto.
> @@ -1552,8 +1556,8 @@ uint64_t HELPER(neon_abdl_u32)(uint32_t a, uint32_t b)
> {
> uint64_t tmp;
> uint64_t result;
> - DO_ABD(result, a, b, uint16_t);
> - DO_ABD(tmp, a >> 16, b >> 16, uint16_t);
> + DO_ABD(result, a, b, uint16_t, uint32_t);
> + DO_ABD(tmp, a >> 16, b >> 16, uint16_t, uint32_t);
> return result | (tmp << 32);
> }
>
> @@ -1561,22 +1565,22 @@ uint64_t HELPER(neon_abdl_s32)(uint32_t a, uint32_t b)
> {
> uint64_t tmp;
> uint64_t result;
> - DO_ABD(result, a, b, int16_t);
> - DO_ABD(tmp, a >> 16, b >> 16, int16_t);
> + DO_ABD(result, a, b, int16_t, int32_t);
> + DO_ABD(tmp, a >> 16, b >> 16, int16_t, int32_t);
> return result | (tmp << 32);
> }
>
> uint64_t HELPER(neon_abdl_u64)(uint32_t a, uint32_t b)
> {
> uint64_t result;
> - DO_ABD(result, a, b, uint32_t);
> + DO_ABD(result, a, b, uint32_t, uint64_t);
> return result;
> }
>
> uint64_t HELPER(neon_abdl_s64)(uint32_t a, uint32_t b)
> {
> uint64_t result;
> - DO_ABD(result, a, b, int32_t);
> + DO_ABD(result, a, b, int32_t, int64_t);
> return result;
> }
> #undef DO_ABD
All the others looks fine.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
aurel...@aurel32.net http://www.aurel32.net
