Re: [PATCH v2 1/1] zlib.c: use size_t for size

> On Sun, Oct 14, 2018 at 03:16:36AM +0100, Ramsay Jones wrote:
> 
>> diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
>> index b059b86aee..3b5f2c38b3 100644
>> --- a/builtin/pack-objects.c
>> +++ b/builtin/pack-objects.c
>> @@ -269,12 +269,12 @@ static void copy_pack_data(struct hashfile *f,
>>  		off_t len)
>>  {
>>  	unsigned char *in;
>> -	unsigned long avail;
>> +	size_t avail;
>>  
>>  	while (len) {
>>  		in = use_pack(p, w_curs, offset, &avail);
>>  		if (avail > len)
>> -			avail = (unsigned long)len;
>> +			avail = xsize_t(len);
> 
> We don't actually care about truncation here. The idea is that we take a
> bite-sized chunk via use_pack, and loop as necessary. So mod-2^32
> truncation via a cast would be bad (we might not make forward progress),
> but truncating to SIZE_MAX would be fine.
> 
> That said, we know that would not truncate here, because we must
> strictly be shrinking "avail", which was already a size_t (unless "len"
> is negative, but then we are really screwed ;) ).
> 
> So I kind of wonder if a comment would be better than xsize_t here.
> Something like:
> 
>   if (avail > len) {
> 	/*
> 	 * This can never truncate because we know that len is smaller
> 	 * than avail, which is already a size_t.
> 	 */
> 	avail = (size_t)len;
>   }