[PATCH v4 6/8] git-compat-util: introduce more size_t helpers

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

We will use them in the next commit.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 git-compat-util.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/git-compat-util.h b/git-compat-util.h
index a508dbe5a35..1f41e5611a1 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -113,6 +113,14 @@
 #define unsigned_mult_overflows(a, b) \
     ((a) && (b) > maximum_unsigned_value_of_type(a) / (a))
 
+/*
+ * 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))
+
 #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;
+}
+
+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))
-- 
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