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Merge pull request #1019 from Techcable/fix/inttypes-overflow

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Signed integer overflow is undefined behavior in C, avoid it in inttypes.c
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Calvin Rose 2022-08-30 23:23:11 -05:00 committed by GitHub
commit f302f87337
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1 changed files with 16 additions and 2 deletions
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18
src/core/inttypes.c
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@ -407,13 +407,26 @@ static Janet cfun_it_u64_compare(int32_t argc, Janet *argv) {
return janet_wrap_nil();
}
/*
* In C, signed arithmetic overflow is undefined behvior
* but unsigned arithmetic overflow is twos complement
*
* Reference:
* https://en.cppreference.com/w/cpp/language/ub
* http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html
*
* This means OPMETHOD & OPMETHODINVERT must always use
* unsigned arithmetic internally, regardless of the true type.
* This will not affect the end result (property of twos complement).
*/
#define OPMETHOD(T, type, name, oper) \
static Janet cfun_it_##type##_##name(int32_t argc, Janet *argv) { \
janet_arity(argc, 2, -1); \
T *box = janet_abstract(&janet_##type##_type, sizeof(T)); \
*box = janet_unwrap_##type(argv[0]); \
for (int32_t i = 1; i < argc; i++) \
*box oper##= janet_unwrap_##type(argv[i]); \
/* This avoids undefined behavior. See above for why. */ \
*box = (T) ((uint64_t) (*box)) oper ((uint64_t) janet_unwrap_##type(argv[i])); \
return janet_wrap_abstract(box); \
} \
@ -422,7 +435,8 @@ static Janet cfun_it_##type##_##name(int32_t argc, Janet *argv) { \
janet_fixarity(argc, 2); \
T *box = janet_abstract(&janet_##type##_type, sizeof(T)); \
*box = janet_unwrap_##type(argv[1]); \
*box oper##= janet_unwrap_##type(argv[0]); \
/* This avoids undefined behavior. See above for why. */ \
*box = (T) ((uint64_t) *box) oper ((uint64_t) janet_unwrap_##type(argv[0])); \
return janet_wrap_abstract(box); \
} \