cast: new limited cast package inspired by Jan Engelhardt's libhx.
authorRusty Russell <rusty@rustcorp.com.au>
Wed, 2 Mar 2011 03:57:07 +0000 (14:27 +1030)
committerRusty Russell <rusty@rustcorp.com.au>
Wed, 2 Mar 2011 03:57:07 +0000 (14:27 +1030)
15 files changed:
ccan/cast/LICENSE [new symlink]
ccan/cast/_info [new file with mode: 0644]
ccan/cast/cast.h [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_const-sizesame.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_const.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_const2-sizesame.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_const2.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_const3-sizesame.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_const3.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_signed-const.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_signed-sizesame.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_signed.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_static-2.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_static-3.c [new file with mode: 0644]
ccan/cast/test/compile_fail-cast_static.c [new file with mode: 0644]

diff --git a/ccan/cast/LICENSE b/ccan/cast/LICENSE
new file mode 120000 (symlink)
index 0000000..7455044
--- /dev/null
@@ -0,0 +1 @@
+../../licenses/LGPL-3
\ No newline at end of file
diff --git a/ccan/cast/_info b/ccan/cast/_info
new file mode 100644 (file)
index 0000000..2dd9b20
--- /dev/null
@@ -0,0 +1,84 @@
+#include <string.h>
+#include "config.h"
+
+/**
+ * cast - routines for safer casting.
+ *
+ * Often you want to cast in a limited way, such as removing a const or
+ * switching between integer types.  However, normal casts will work on
+ * almost any type, making them dangerous when the code changes.
+ *
+ * These C++-inspired macros serve two purposes: they make it clear the
+ * exact reason for the cast, and they also (with some compilers) cause
+ * errors when misused.
+ *
+ * Based on Jan Engelhardt's libHX macros: http://libhx.sourceforge.net/
+ *
+ * Author: Jan Engelhardt
+ * Maintainer: Rusty Russell <rusty@rustcorp.com.au>
+ * License: LGPL
+ *
+ * Example:
+ *     // Given "test" contains "3 t's in 'test string'
+ *     #include <ccan/cast/cast.h>
+ *     #include <stdint.h>
+ *     #include <stdio.h>
+ *
+ *     // Find char @orig in @str, if @repl, replace them.  Return number.
+ *     static size_t find_chars(char *str, char orig, char repl)
+ *     {
+ *             size_t i, count = 0;
+ *             for (i = 0; str[i]; i++) {
+ *                     if (str[i] == orig) {
+ *                             count++;
+ *                             if (repl)
+ *                                     str[i] = repl;
+ *                     }
+ *             }
+ *             return count;
+ *     }
+ *
+ *     // Terrible hash function.
+ *     static uint64_t hash_string(const unsigned char *str)
+ *     {
+ *             size_t i;
+ *             uint64_t hash = 0;
+ *             for (i = 0; str[i]; i++)
+ *                     hash += str[i];
+ *             return hash;
+ *     }
+ *
+ *     int main(int argc, char *argv[])
+ *     {
+ *             uint64_t hash;
+ *
+ *             // find_chars wants a non-const string, but doesn't
+ *             // need it if repl == 0.
+ *             printf("%zu %c's in 'test string'\n",
+ *                    find_chars(cast_const(char *, "test string"),
+ *                               argv[1][0], 0),
+ *                    argv[1][0]);
+ *
+ *             // hash_string wants an unsigned char.
+ *             hash = hash_string(cast_signed(unsigned char *, argv[1]));
+ *
+ *             // Need a long long to hand to printf.
+ *             printf("Hash of '%s' = %llu\n", argv[1],
+ *                    cast_static(unsigned long long, hash));
+ *             return 0;
+ *     }
+ *             
+ */
+int main(int argc, char *argv[])
+{
+       /* Expect exactly one argument */
+       if (argc != 2)
+               return 1;
+
+       if (strcmp(argv[1], "depends") == 0) {
+               printf("ccan/build_assert\n");
+               return 0;
+       }
+
+       return 1;
+}
diff --git a/ccan/cast/cast.h b/ccan/cast/cast.h
new file mode 100644 (file)
index 0000000..f3bb445
--- /dev/null
@@ -0,0 +1,131 @@
+#ifndef CCAN_CAST_H
+#define CCAN_CAST_H
+#include "config.h"
+#include <ccan/build_assert/build_assert.h>
+
+/**
+ * cast_signed - cast a (const) char * to/from (const) signed/unsigned char *.
+ * @type: some char * variant.
+ * @expr: expression (of some char * variant) to cast.
+ *
+ * Some libraries insist on an unsigned char in various places; cast_signed
+ * makes sure (with suitable compiler) that the expression you are casting
+ * only differs in signed/unsigned, not in type or const-ness.
+ */
+#define cast_signed(type, expr)                                                \
+       ((type)(expr)                                                   \
+        + EXPR_BUILD_ASSERT(cast_sign_compatible(type, (expr))))
+
+/**
+ * cast_const - remove a const qualifier from a pointer.
+ * @type: some pointer type.
+ * @expr: expression to cast.
+ *
+ * This ensures that you are only removing the const qualifier from an
+ * expression.  The expression must otherwise match @type.
+ *
+ * If @type is a pointer to a pointer, you must use cast_const2 (etc).
+ *
+ * Example:
+ *     // Dumb open-coded strstr variant.
+ *     static char *find_needle(const char *haystack)
+ *     {
+ *             size_t i;
+ *             for (i = 0; i < strlen(haystack); i++)
+ *             if (memcmp("needle", haystack+i, strlen("needle")) == 0)
+ *                     return cast_const(char *, haystack+i);
+ *             return NULL;
+ *     }
+ */
+#define cast_const(type, expr)                                 \
+       ((type)(expr)                                           \
+        + EXPR_BUILD_ASSERT(cast_const_compat1((expr), type)))
+
+/**
+ * cast_const2 - remove a const qualifier from a pointer to a pointer.
+ * @type: some pointer to pointer type.
+ * @expr: expression to cast.
+ *
+ * This ensures that you are only removing the const qualifier from an
+ * expression.  The expression must otherwise match @type.
+ */
+#define cast_const2(type, expr)                                        \
+       ((type)(expr)                                           \
+        + EXPR_BUILD_ASSERT(cast_const_compat2((expr), type)))
+
+/**
+ * cast_const3 - remove a const from a pointer to a pointer to a pointer..
+ * @type: some pointer to pointer to pointer type.
+ * @expr: expression to cast.
+ *
+ * This ensures that you are only removing the const qualifier from an
+ * expression.  The expression must otherwise match @type.
+ */
+#define cast_const3(type, expr)                                        \
+       ((type)(expr)                                           \
+        + EXPR_BUILD_ASSERT(cast_const_compat3((expr), type)))
+
+
+/**
+ * cast_static - explicit mimic of implicit cast.
+ * @type: some type.
+ * @expr: expression to cast.
+ *
+ * This ensures that the cast is not to or from a pointer: it can only be
+ * an implicit cast, such as a pointer to a similar const pointer, or between
+ * integral types.
+ */
+#if HAVE_COMPOUND_LITERALS
+#define cast_static(type, expr)                        \
+       ((struct { type x; }){(expr)}.x)
+#else
+#define cast_static(type, expr)                        \
+       ((type)(expr))
+#endif
+
+/* Herein lies the gcc magic to evoke compile errors. */
+#if HAVE_BUILTIN_CHOOSE_EXPR && HAVE_BUILTIN_TYPES_COMPATIBLE_P && HAVE_TYPEOF
+#define cast_sign_compatible(t, e) \
+  __builtin_choose_expr(                                               \
+         __builtin_types_compatible_p(__typeof__(t), char *) ||        \
+         __builtin_types_compatible_p(__typeof__(t), signed char *) || \
+         __builtin_types_compatible_p(__typeof__(t), unsigned char *), \
+         /* if type is not const qualified */                          \
+         __builtin_types_compatible_p(__typeof__(e), char *) ||        \
+         __builtin_types_compatible_p(__typeof__(e), signed char *) || \
+         __builtin_types_compatible_p(__typeof__(e), unsigned char *), \
+         /* and if it is... */                                         \
+         __builtin_types_compatible_p(__typeof__(e), const char *) ||  \
+         __builtin_types_compatible_p(__typeof__(e), const signed char *) || \
+         __builtin_types_compatible_p(__typeof__(e), const unsigned char *) ||\
+         __builtin_types_compatible_p(__typeof__(e), char *) ||        \
+         __builtin_types_compatible_p(__typeof__(e), signed char *) || \
+         __builtin_types_compatible_p(__typeof__(e), unsigned char *)  \
+         )
+
+#define cast_const_strip1(expr)                        \
+       __typeof__(*(struct { int z; __typeof__(expr) x; }){0}.x)
+#define cast_const_strip2(expr) \
+       __typeof__(**(struct { int z; __typeof__(expr) x; }){0}.x)
+#define cast_const_strip3(expr) \
+       __typeof__(***(struct { int z; __typeof__(expr) x; }){0}.x)
+#define cast_const_compat1(expr, type)                                 \
+       __builtin_types_compatible_p(cast_const_strip1(expr),           \
+                                    cast_const_strip1(type))
+#define cast_const_compat2(expr, type)                                 \
+       __builtin_types_compatible_p(cast_const_strip2(expr),           \
+                                    cast_const_strip2(type))
+#define cast_const_compat3(expr, type)                                 \
+       __builtin_types_compatible_p(cast_const_strip3(expr),           \
+                                    cast_const_strip3(type))
+#else
+#define cast_sign_compatible(type, expr)               \
+       (sizeof(*(type)0) == 1 && sizeof(*(expr)) == 1)
+#define cast_const_compat1(expr, type)         \
+       (sizeof(*(expr)) == sizeof(*(type)0))
+#define cast_const_compat2(expr, type)         \
+       (sizeof(**(expr)) == sizeof(**(type)0))
+#define cast_const_compat3(expr, type)                 \
+       (sizeof(***(expr)) == sizeof(***(type)0))
+#endif
+#endif /* CCAN_CAST_H */
diff --git a/ccan/cast/test/compile_fail-cast_const-sizesame.c b/ccan/cast/test/compile_fail-cast_const-sizesame.c
new file mode 100644 (file)
index 0000000..d401cc8
--- /dev/null
@@ -0,0 +1,28 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+/* Note: this *isn't* sizeof(char) on all platforms. */
+struct char_struct {
+       char c;
+};
+
+int main(int argc, char *argv[])
+{
+       char *uc;
+       const
+#ifdef FAIL
+               struct char_struct
+#else
+               char
+#endif
+               *p = NULL;
+
+       uc = cast_const(char *, p);
+       return 0;
+}
+
+#ifdef FAIL
+#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
+#error "Unfortunately we don't fail if cast_const can only use size"
+#endif
+#endif
diff --git a/ccan/cast/test/compile_fail-cast_const.c b/ccan/cast/test/compile_fail-cast_const.c
new file mode 100644 (file)
index 0000000..bb8de94
--- /dev/null
@@ -0,0 +1,17 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+       char *uc;
+       const 
+#ifdef FAIL
+               int
+#else
+               char
+#endif
+               *p = NULL;
+
+       uc = cast_const(char *, p);
+       return 0;
+}
diff --git a/ccan/cast/test/compile_fail-cast_const2-sizesame.c b/ccan/cast/test/compile_fail-cast_const2-sizesame.c
new file mode 100644 (file)
index 0000000..a16cfac
--- /dev/null
@@ -0,0 +1,28 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+/* Note: this *isn't* sizeof(char) on all platforms. */
+struct char_struct {
+       char c;
+};
+
+int main(int argc, char *argv[])
+{
+       char **uc;
+       const
+#ifdef FAIL
+               struct char_struct
+#else
+               char
+#endif
+               **p = NULL;
+
+       uc = cast_const2(char **, p);
+       return 0;
+}
+
+#ifdef FAIL
+#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
+#error "Unfortunately we don't fail if cast_const can only use size"
+#endif
+#endif
diff --git a/ccan/cast/test/compile_fail-cast_const2.c b/ccan/cast/test/compile_fail-cast_const2.c
new file mode 100644 (file)
index 0000000..88df4b7
--- /dev/null
@@ -0,0 +1,17 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+       char **uc;
+       const 
+#ifdef FAIL
+               int
+#else
+               char
+#endif
+               **p = NULL;
+
+       uc = cast_const2(char **, p);
+       return 0;
+}
diff --git a/ccan/cast/test/compile_fail-cast_const3-sizesame.c b/ccan/cast/test/compile_fail-cast_const3-sizesame.c
new file mode 100644 (file)
index 0000000..f782f9d
--- /dev/null
@@ -0,0 +1,28 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+/* Note: this *isn't* sizeof(char) on all platforms. */
+struct char_struct {
+       char c;
+};
+
+int main(int argc, char *argv[])
+{
+       char ***uc;
+       const
+#ifdef FAIL
+               struct char_struct
+#else
+               char
+#endif
+               ***p = NULL;
+
+       uc = cast_const3(char ***, p);
+       return 0;
+}
+
+#ifdef FAIL
+#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
+#error "Unfortunately we don't fail if cast_const can only use size"
+#endif
+#endif
diff --git a/ccan/cast/test/compile_fail-cast_const3.c b/ccan/cast/test/compile_fail-cast_const3.c
new file mode 100644 (file)
index 0000000..6232c86
--- /dev/null
@@ -0,0 +1,17 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+       char ***uc;
+       const 
+#ifdef FAIL
+               int
+#else
+               char
+#endif
+               ***p = NULL;
+
+       uc = cast_const3(char ***, p);
+       return 0;
+}
diff --git a/ccan/cast/test/compile_fail-cast_signed-const.c b/ccan/cast/test/compile_fail-cast_signed-const.c
new file mode 100644 (file)
index 0000000..4e67dc6
--- /dev/null
@@ -0,0 +1,15 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+       unsigned char *uc;
+#ifdef FAIL
+       const
+#endif
+       char
+               *p = NULL;
+
+       uc = cast_signed(unsigned char *, p);
+       return 0;
+}
diff --git a/ccan/cast/test/compile_fail-cast_signed-sizesame.c b/ccan/cast/test/compile_fail-cast_signed-sizesame.c
new file mode 100644 (file)
index 0000000..87da721
--- /dev/null
@@ -0,0 +1,28 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+/* Note: this *isn't* sizeof(char) on all platforms. */
+struct char_struct {
+       char c;
+};
+
+int main(int argc, char *argv[])
+{
+       unsigned char *uc;
+#ifdef FAIL
+       struct char_struct
+#else
+       char
+#endif
+               *p = NULL;
+
+       uc = cast_signed(unsigned char *, p);
+
+       return 0;
+}
+
+#ifdef FAIL
+#if !HAVE_TYPEOF||!HAVE_BUILTIN_CHOOSE_EXPR||!HAVE_BUILTIN_TYPES_COMPATIBLE_P
+#error "Unfortunately we don't fail if cast_signed can only use size"
+#endif
+#endif
diff --git a/ccan/cast/test/compile_fail-cast_signed.c b/ccan/cast/test/compile_fail-cast_signed.c
new file mode 100644 (file)
index 0000000..5b182ab
--- /dev/null
@@ -0,0 +1,16 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+       unsigned char *uc;
+#ifdef FAIL
+       int
+#else
+       char
+#endif
+               *p = NULL;
+
+       uc = cast_signed(unsigned char *, p);
+       return 0;
+}
diff --git a/ccan/cast/test/compile_fail-cast_static-2.c b/ccan/cast/test/compile_fail-cast_static-2.c
new file mode 100644 (file)
index 0000000..d3ba8d3
--- /dev/null
@@ -0,0 +1,22 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+       char *c;
+#ifdef FAIL
+       long
+#else
+       char
+#endif
+               *p = 0;
+
+       c = cast_static(char *, p);
+       return 0;
+}
+
+#ifdef FAIL
+#if !HAVE_COMPOUND_LITERALS
+#error "Unfortunately we don't fail if cast_static is a noop"
+#endif
+#endif
diff --git a/ccan/cast/test/compile_fail-cast_static-3.c b/ccan/cast/test/compile_fail-cast_static-3.c
new file mode 100644 (file)
index 0000000..1625f54
--- /dev/null
@@ -0,0 +1,20 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+       char *c;
+#ifdef FAIL
+       const
+#endif
+               char *p = 0;
+
+       c = cast_static(char *, p);
+       return 0;
+}
+
+#ifdef FAIL
+#if !HAVE_COMPOUND_LITERALS
+#error "Unfortunately we don't fail if cast_static is a noop"
+#endif
+#endif
diff --git a/ccan/cast/test/compile_fail-cast_static.c b/ccan/cast/test/compile_fail-cast_static.c
new file mode 100644 (file)
index 0000000..51ea8c2
--- /dev/null
@@ -0,0 +1,16 @@
+#include <ccan/cast/cast.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+       char c;
+#ifdef FAIL
+       char *
+#else
+       long
+#endif
+               x = 0;
+
+       c = cast_static(char, x);
+       return 0;
+}