Re: [PATCH] scan-converter: Explicitly cast to int when flooring

Might be an compiler issue?

Henry

> On Sep 11, 2015, at 8:22 AM, Uli Schlachter <[email protected]> wrote:
> 
> Am 10.09.2015 um 20:56 schrieb Bryce Harrington:
>> The code in question is attempting to do x*a/b, however for sufficiently
>> large x and a, this can exceed integer limits; the code accounts for
>> this by casting x*a to a long long.  However, when then assigning this
>> value to our quorem value this results in an implicit cast to int, which
>> valgrind flags as an 'invalid write'.
> 
> ...?!?
> 
> How can an implicit cast cause an invalid write for valgrind? Wouldn't an
> explicit cast have the exact same effect as an implicit one here?
> 
> Uli
> 
>> Signed-off-by: Bryce Harrington <[email protected]>
>> ---
>> src/cairo-botor-scan-converter.c    | 4 ++--
>> src/cairo-clip-tor-scan-converter.c | 4 ++--
>> src/cairo-mono-scan-converter.c     | 4 ++--
>> src/cairo-tor22-scan-converter.c    | 4 ++--
>> 4 files changed, 8 insertions(+), 8 deletions(-)
>> 
>> diff --git a/src/cairo-botor-scan-converter.c b/src/cairo-botor-scan-converter.c
>> index 515305b..b76d2fa 100644
>> --- a/src/cairo-botor-scan-converter.c
>> +++ b/src/cairo-botor-scan-converter.c
>> @@ -199,8 +199,8 @@ floored_muldivrem(int x, int a, int b)
>> {
>>    struct quorem qr;
>>    long long xa = (long long)x*a;
>> -    qr.quo = xa/b;
>> -    qr.rem = xa%b;
>> +    qr.quo = (int32_t)(xa/b);
>> +    qr.rem = (int32_t)(xa%b);
>>    if ((xa>=0) != (b>=0) && qr.rem) {
>> 	qr.quo--;
>> 	qr.rem += b;
>> diff --git a/src/cairo-clip-tor-scan-converter.c b/src/cairo-clip-tor-scan-converter.c
>> index e32a5a9..ac581da 100644
>> --- a/src/cairo-clip-tor-scan-converter.c
>> +++ b/src/cairo-clip-tor-scan-converter.c
>> @@ -439,8 +439,8 @@ floored_muldivrem(int x, int a, int b)
>> {
>>    struct quorem qr;
>>    long long xa = (long long)x*a;
>> -    qr.quo = xa/b;
>> -    qr.rem = xa%b;
>> +    qr.quo = (int32_t)(xa/b);
>> +    qr.rem = (int32_t)(xa%b);
>>    if ((xa>=0) != (b>=0) && qr.rem) {
>> 	qr.quo -= 1;
>> 	qr.rem += b;
>> diff --git a/src/cairo-mono-scan-converter.c b/src/cairo-mono-scan-converter.c
>> index 2a9546c..1040cad 100644
>> --- a/src/cairo-mono-scan-converter.c
>> +++ b/src/cairo-mono-scan-converter.c
>> @@ -107,8 +107,8 @@ floored_muldivrem(int x, int a, int b)
>> {
>>    struct quorem qr;
>>    long long xa = (long long)x*a;
>> -    qr.quo = xa/b;
>> -    qr.rem = xa%b;
>> +    qr.quo = (int32_t)(xa/b);
>> +    qr.rem = (int32_t)(xa%b);
>>    if ((xa>=0) != (b>=0) && qr.rem) {
>> 	qr.quo -= 1;
>> 	qr.rem += b;
>> diff --git a/src/cairo-tor22-scan-converter.c b/src/cairo-tor22-scan-converter.c
>> index 4cec5ee..e7f72cd 100644
>> --- a/src/cairo-tor22-scan-converter.c
>> +++ b/src/cairo-tor22-scan-converter.c
>> @@ -478,8 +478,8 @@ floored_muldivrem(int x, int a, int b)
>> {
>>    struct quorem qr;
>>    long long xa = (long long)x*a;
>> -    qr.quo = xa/b;
>> -    qr.rem = xa%b;
>> +    qr.quo = (int32_t)(xa/b);
>> +    qr.rem = (int32_t)(xa%b);
>>    if ((xa>=0) != (b>=0) && qr.rem) {
>> 	qr.quo -= 1;
>> 	qr.rem += b;
>> 
> 
> 
> -- 
> - He made himself, me nothing, you nothing out of the dust
> - Er machte sich mir nichts, dir nichts aus dem Staub
> -- 
> cairo mailing list
> [email protected]
> http://lists.cairographics.org/mailman/listinfo/cairo

-- 
cairo mailing list
[email protected]
http://lists.cairographics.org/mailman/listinfo/cairo