diff mbox series

[v3,6/8] git-compat-util: introduce more size_t helpers

Message ID 18419070c29aef85c266f01174f436566bf792fd.1635515959.git.gitgitgadget@gmail.com (mailing list archive)
State New, archived
Headers show
Series Allow clean/smudge filters to handle huge files in the LLP64 data model | expand

Commit Message

Johannes Schindelin Oct. 29, 2021, 1:59 p.m. UTC 
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(+)

Comments

Junio C Hamano Oct. 29, 2021, 11:10 p.m. UTC | #1 
"Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
writes:

> +/*
> + * 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.

>  #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.

> +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))
diff mbox series

Patch

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))