Hi Dscho, On Thu, Sep 26, 2019 at 01:30:10AM -0700, Johannes Schindelin via GitGitGadget wrote: > From: Johannes Schindelin <johannes.schindelin@xxxxxx> > > MSVC complains about this with `-Wall`, which can be taken as a sign > that this is indeed a real bug. The symptom is: > > C4146: unary minus operator applied to unsigned type, result > still unsigned > > Let's avoid this warning in the minimal way, e.g. writing `-1 - > <unsigned value>` instead of `-<unsigned value> - 1`. [...] > --- > read-cache.c | 4 ++-- > sha1-lookup.c | 2 +- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/read-cache.c b/read-cache.c > index c701f7f8b8..11f3357216 100644 > --- a/read-cache.c > +++ b/read-cache.c > @@ -1276,7 +1276,7 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e > */ > if (istate->cache_nr > 0 && > strcmp(ce->name, istate->cache[istate->cache_nr - 1]->name) > 0) > - pos = -istate->cache_nr - 1; > + pos = -1 - istate->cache_nr; I've been thinking about this and I'm still not certain that this 100% correct from a language-lawyer perspective. If we do `-1 - istate->cache_nr`, then the unsignedness of istate->cache_nr takes over and the whole expression is a very large unsigned number. Then, when we assign to `int pos`, we are converting an unsigned number which is out of the range of the signed number. According to a StackOverflow post citing the C99 standard[1]: Otherwise, the new type is signed and the value cannot be represented in it; either the result is implementation-defined or an implementation-defined signal is raised. I'm sure that most platforms that we support will handle it sanely but could we write this as pos = -1 - (int) istate->cache_nr; to be doubly sure that no funny business will happen? > else > pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce)); > > @@ -1894,7 +1894,7 @@ static size_t estimate_cache_size(size_t ondisk_size, unsigned int entries) > /* > * Account for potential alignment differences. > */ > - per_entry += align_padding_size(sizeof(struct cache_entry), -sizeof(struct ondisk_cache_entry)); > + per_entry += align_padding_size(per_entry, 0); > return ondisk_size + entries * per_entry; > } > > diff --git a/sha1-lookup.c b/sha1-lookup.c > index 796ab68da8..c819687730 100644 > --- a/sha1-lookup.c > +++ b/sha1-lookup.c > @@ -97,7 +97,7 @@ int sha1_pos(const unsigned char *sha1, void *table, size_t nr, > lo = mi + 1; > mi = lo + (hi - lo) / 2; > } while (lo < hi); > - return -lo-1; > + return -1 - lo; Same thing here. [1]: https://stackoverflow.com/questions/50605/signed-to-unsigned-conversion-in-c-is-it-always-safe > } > > int bsearch_hash(const unsigned char *sha1, const uint32_t *fanout_nbo, > -- > gitgitgadget >
