git-compat-util.h: drop u64_add(), u64_mult() helpers

The u64_add() and u64_mult() helper functions were introduced in
b103881 (midx repack: avoid integer overflow on 32 bit systems,
2025-05-22) to implement overflow checks during a fixed-point
calculation when estimating pack sizes in the MIDX writing code.

However, those functions call die() when either the addition or
multiplication of their operands (depending on which function is being
called) would cause an overflow. This does not allow the caller to
provide a more detailed message, presenting the user with an opaque
message like:

    fatal: uint64_t overflow: M * N

Let's discourage these opaque error messages by dropping these functions
entirely and instead having the caller use unsigned_mult_overflows() or
unsigned_add_overflows() themselves, providing the caller the
opportunity to come up with their own die() message.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>

Author: ttaylorr

git-compat-util.h

@@ -641,22 +641,6 @@ static inline int cast_size_t_to_int(size_t a)
 	return (int)a;
 }
 
-static inline uint64_t u64_mult(uint64_t a, uint64_t b)
-{
-	if (unsigned_mult_overflows(a, b))
-		die("uint64_t overflow: %"PRIuMAX" * %"PRIuMAX,
-		    (uintmax_t)a, (uintmax_t)b);
-	return a * b;
-}
-
-static inline uint64_t u64_add(uint64_t a, uint64_t b)
-{
-	if (unsigned_add_overflows(a, b))
-		die("uint64_t overflow: %"PRIuMAX" + %"PRIuMAX,
-		    (uintmax_t)a, (uintmax_t)b);
-	return a + b;
-}
-
 /*
  * Limit size of IO chunks, because huge chunks only cause pain.  OS X
  * 64-bit is buggy, returning EINVAL if len >= INT_MAX; and even in

midx-write.c

@@ -1738,8 +1738,19 @@ static void fill_included_packs_batch(struct repository *r,
 		 */
 		expected_size = (uint64_t)pack_info[i].referenced_objects << 14;
 		expected_size /= p->num_objects;
-		expected_size = u64_mult(expected_size, p->pack_size);
-		expected_size = u64_add(expected_size, 1u << 13) >> 14;
+
+		if (unsigned_mult_overflows(expected_size,
+					    (uint64_t)p->pack_size))
+			die(_("overflow during fixed-point multiply (%"PRIu64" "
+			      "* %"PRIu64")"),
+			    expected_size, (uint64_t)p->pack_size);
+		expected_size = expected_size * p->pack_size;
+
+		if (unsigned_add_overflows(expected_size, 1u << 13))
+			die(_("overflow during fixed-point rounding (%"PRIu64" "
+			      " + %"PRIu64")"),
+			    expected_size, (uint64_t)(1ul << 13));
+		expected_size = (expected_size + (1u << 13)) >> 14;
 
 		if (expected_size >= batch_size)
 			continue;