Re: [PATCH v3 6/8] git-compat-util: introduce more size_t helpers
From: Junio C Hamano <hidden>
Date: 2021-10-29 23:10:36
"Johannes Schindelin via GitGitGadget" [off-list ref] writes:
quoted hunk
+/* + * Returns true if the left shift of "a" by "shift" bits will + * overflow. The type of "a" must be unsigned. + */ +#define unsigned_left_shift_overflows(a, shift) \ + ((shift) < bitsizeof(a) && \ + (a) > maximum_unsigned_value_of_type(a) >> (shift))
Cute. So somebody asks
if (unsigned_left_shift_overflows(a, 100)
and they get "you are unsafe, regardless of the value of a, you get
an overflow". Makes perfect sensen.
quoted hunk
#ifdef __GNUC__ #define TYPEOF(x) (__typeof__(x)) #else@@ -859,6 +867,23 @@ static inline size_t st_sub(size_t a, size_t b) return a - b; } +static inline size_t st_left_shift(size_t a, unsigned shift) +{ + if (unsigned_left_shift_overflows(a, shift)) + die("size_t overflow: %"PRIuMAX" << %u", + (uintmax_t)a, shift); + return a << shift; +}
Makes sense.
quoted hunk
+static inline unsigned long cast_size_t_to_ulong(size_t a) +{ + if (a != (unsigned long)a) + die("object too large to read on this platform: %" + PRIuMAX" is cut off to %lu", + (uintmax_t)a, (unsigned long)a); + return (unsigned long)a; +} + #ifdef HAVE_ALLOCA_H # include <alloca.h> # define xalloca(size) (alloca(size))