--- /dev/null
+#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;
+}
--- /dev/null
+#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 */
projects / ccan / commitdiff