X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~mdw/git/mLib/blobdiff_plain/e6591bec0938b76b8c02083eb6ba101aba4e1b7e..08bb7015a9e28c5c9d38fe05a6f6644bc21fa527:/utils/macros.h

diff --git a/utils/macros.h b/utils/macros.h
index 73230bd..2ca5a06 100644
--- a/utils/macros.h
+++ b/utils/macros.h
@@ -42,25 +42,144 @@
 
 /*----- Miscellaneous utility macros --------------------------------------*/
 
+/* --- @N@ --- *
+ *
+ * Arguments:	@type v[]@ = an actual array, not a pointer
+ *
+ * Returns:	The number of elements in @v@.
+ */
+
 #define N(v) (sizeof(v)/sizeof(*(v)))
 
+/* --- @STR@ --- *
+ *
+ * Arguments:	@x@ = some tokens
+ *
+ * Returns:	A string literal containing the macro-expanded text of @x@.
+ */
+
 #define MLIB__STR(x) #x
 #define STR(x) MLIB__STR(x)
 
+/* --- @GLUE@, @GLUE3@ --- *
+ *
+ * Arguments:	@x, y@ = two sequences of tokens
+ *		@z@ = a third sequence of tokens
+ *
+ * Returns:	A single token formed by gluing together the macro-expansions
+ *		of @x@ and @y@, and @z@ for @GLUE3@.
+ */
+
 #define MLIB__GLUE(x, y) x##y
 #define GLUE(x, y) MLIB__GLUE(x, y)
+#define GLUE3(x, y, z) GLUE(x, MLIB__GLUE(y, z))
+
+/* --- @STATIC_ASSERT@ --- *
+ *
+ * Arguments:	@int cond@ = a condition
+ *		@msg@ = a string literal message
+ *
+ * Returns:	---
+ *
+ * Use:		Fail at compile time unless @cond@ is nonzero.  The failure
+ *		might report @msg@.
+ */
 
 #ifdef static_assert
 #  define STATIC_ASSERT(cond, msg) static_assert(!!(cond), msg)
 #else
 #  define STATIC_ASSERT(cond, msg)					\
-	IGNORABLE extern char static_assert_failed[2*!!(cond) - 1]
+	IGNORABLE extern char static_assert_failed[1 - 2*!(cond)]
 #endif
 
+/* --- @CHECK_TYPE@ ---
+ *
+ * Arguments:	@expty@ = expected type of @x@
+ *		@expty x@ = some object
+ *
+ * Returns:	Integer zero.
+ *
+ * Use:		Cause a compile-time failure unless the type of @x@ is
+ *		assignment-compatible with @expty@.
+ */
+
+#define CHECK_TYPE(expty, x) (!sizeof(*(expty *)0 = (x)))
+
+/* --- @CONVERT_CAREFULLY@ ---
+ *
+ * Arguments:	@newty@ = new type for the result
+ *		@expty@ = expected type of @x@
+ *		@expty x@ = some object
+ *
+ * Returns:	@x@, but coerced to type @newty@.
+ *
+ * Use:		Like @(newty)x@, except that it checks at compile-time that
+ *		@x@ is at least assignment-compatible with type @expty@
+ *		before trying.
+ */
+
+#define CONVERT_CAREFULLY(newty, expty, x)				\
+	(CHECK_TYPE(expty, x) + (/*unconst unvolatile*/ newty)(x))
+
+/* --- @UNCONST@, @UNVOLATILE@, @UNQUALIFY@ --- *
+ *
+ * Arguments:	@type@ = a type name
+ *		@type *p@ = a pointer
+ *
+ * Returns:	@p@, but without @const@, @volatile@ or both qualifiers.
+ *
+ * Use:		Strips qualifiers from pointer types.
+ *
+ *		The @UNCONST@ macro strips @const@.  It checks that @p@
+ *		has type `pointer to @type@ or @const type@'; if not, a
+ *		compile-time error results.  Otherwise, it returns the value
+ *		of @p@, converted to `pointer to (non-constant) @type@'.  It
+ *		will not silently strip a @volatile@ qualifier.
+ *
+ *		The @UNVOLATILE@ macro is similar, except that it strips
+ *		@volatile@ instead of @const@.  The @UNQUALIFY@ macro strips
+ *		both qualifiers.
+ */
+
+#define UNCONST(type, p) CONVERT_CAREFULLY(type *, const type *, p)
+#define UNVOLATILE(type, p) CONVERT_CAREFULLY(type *, volatile type *, p)
+#define UNQUALIFY(type, p)						\
+	CONVERT_CAREFULLY(type *, const volatile type *, p)
+
+/* --- @EMPTY@ --- *
+ *
+ * Arguments:	---
+ *
+ * Returns:	The empty token sequence.
+ */
+
+#define EMPTY
+
+/* --- @COMMA@ --- *
+ *
+ * Arguments:	---
+ *
+ * Returns:	A `%|,|%' token, which can be usefully passed to macros to
+ *		avoid argument splitting.
+ */
+
 #define COMMA ,
 
 /*----- String and character hacks ----------------------------------------*/
 
+/* --- @IS...@ --- *
+ *
+ * Arguments:	@int ch@ = a character code, but not @EOF@
+ *
+ * Returns:	Nonzero if @ch@ is in the relevant @<ctype.h>@ category.
+ *
+ * Use:		Classifies characters, but safely even if characters are
+ *		signed.
+ *
+ *		There is a macro for each of the @<ctype.h>@ @is...@
+ *		functions.
+ */
+
 #define CTYPE_HACK(func, ch) (func((unsigned char)(ch)))
 
 #define ISALNUM(ch) CTYPE_HACK(isalnum, ch)
@@ -77,17 +196,47 @@
 #define ISUPPER(ch) CTYPE_HACK(isupper, ch)
 #define ISXDIGIT(ch) CTYPE_HACK(isxdigit, ch)
 
+/* --- @TO...@ --- *
+ *
+ * Arguments:	@int ch@ = a character code, but not @EOF@
+ *
+ * Returns:	The converted character code.
+ *
+ * Use:		Converts characters, but safely even if characters are
+ *		signed.
+ *
+ *		There is a macro for each of the @<ctype.h>@ @to...@
+ *		functions.
+ */
+
 #define TOASCII(ch) CTYPE_HACK(toascii, ch)
 #define TOLOWER(ch) CTYPE_HACK(tolower, ch)
 #define TOUPPER(ch) CTYPE_HACK(toupper, ch)
 
+/* --- @MEMCMP@, @STRCMP@, @STRNCMP@ --- *
+ *
+ * Arguments:	@const type *x, *y@ = pointers to strings
+ *		@op@ = a relational operator symbol
+ *		@size_t n@ = length of the strings
+ *
+ * Returns:	Nonzero if the relationship between the strings satisfies the
+ *		operator @op@, otherwise zero.
+ *
+ * Use:		These macros mitigate the author's frequent error of failing
+ *		to compare the result of the underlying standard functions
+ *		against zero, effectively reversing the sense of an intended
+ *		test for equality.
+ */
+
 #define MEMCMP(x, op, y, n) (memcmp((x), (y), (n)) op 0)
 #define STRCMP(x, op, y) (strcmp((x), (y)) op 0)
 #define STRNCMP(x, op, y, n) (strncmp((x), (y), (n)) op 0)
 
-/*----- Compiler diagnostics ----------------------------------------------*/
+/*----- Compiler-specific definitions -------------------------------------*/
 
-/* --- Compiler-specific definitions --- */
+/* The descriptions of these are given below, with the fallback
+ * definitions.
+ */
 
 #if GCC_VERSION_P(2, 5) || CLANG_VERSION_P(3, 3)
 #  define NORETURN __attribute__((__noreturn__))
@@ -110,6 +259,16 @@
 #  define EXECL_LIKE(ntrail) __attribute__((__sentinel__(ntrail)))
 #endif
 
+#if GCC_VERSION_P(2, 7) || CLANG_VERSION_P(0, 0)
+#  define LAUNDER(x)							\
+	({ __typeof__(x) _y; __asm__("" : "=g"(_y) : "0"(x)); _y; })
+#  define ADMIRE(x)							\
+	({ __asm__("" :: "g"(x)); })
+#  define ADMIRE_BUF(p, sz)						\
+	({ __asm__("" :: "m"(*(unsigned char *)p), "g"(sz) : "memory"); })
+#  define RELAX do __asm__(""); while (0)
+#endif
+
 #if CLANG_VERSION_P(3, 3)
 
 #  define MLIB__PRAGMA_HACK(x) _Pragma(#x)
@@ -127,7 +286,9 @@
 #  define MUFFLE_WARNINGS_STMT(warns, body)				\
 	do { MLIB__MUFFLE_WARNINGS(warns, body) } while (0)
 
-#elif GCC_VERSION_P(4, 6)
+#endif
+
+#if GCC_VERSION_P(4, 6)
 
    /* --- Diagnostic suppression in GCC: a tale of woe --- *
     *
@@ -185,40 +346,102 @@
 
 /* --- Fallback definitions, mostly trivial --- */
 
-#ifndef DEPRECATED
-#  define DEPRECATED(msg)
-#endif
-
-#ifndef EXECL_LIKE
-#  define EXECL_LIKE(ntrail)
-#endif
+/* --- @DISCARD@ --- *
+ *
+ * Arguments:	@x@ = a function call
+ *
+ * Returns:	---
+ *
+ * Use:		Explicitly discard the result of @x@.  This counteracts a
+ *		@MUST_CHECK@ attribute on the called function.
+ */
 
 #ifndef DISCARD
 #  define DISCARD(x) do if (x); while (0)
 #endif
 
+/* --- @IGNORE@ --- *
+ *
+ * Arguments:	@x@ = any expression
+ *
+ * Returns:	---
+ *
+ * Use:		Ignore the value of @x@, overriding compiler warnings.
+ */
+
 #ifndef IGNORE
 #  define IGNORE(x) ((void)(x))
 #endif
 
-#ifndef MUFFLE_WARNINGS_DECL
-#  define MUFFLE_WARNINGS_DECL(warns, body) body
-#endif
+/* --- @LAUNDER@ --- *
+ *
+ * Arguments:	@x@ = some integer expression
+ *
+ * Returns:	@x@.
+ *
+ * Use:		Causes a compiler to know nothing about the value of @x@,
+ *		even if it looks obvious, e.g., it's a constant.
+ */
 
-#ifndef MUFFLE_WARNINGS_EXPR
-#  define MUFFLE_WARNINGS_EXPR(warns, body) (body)
+#ifndef LAUNDER
+#  define LAUNDER(x) (x)
 #endif
 
-#ifndef MUFFLE_WARNINGS_STMT
-#  define MUFFLE_WARNINGS_STMT(warns, body) do { body } while (0)
+/* --- @ADMIRE@, @ADMIRE_BUF@ --- *
+ *
+ * Arguments:	@x@ = some scalar expression
+ *		@const void *p@, @size_t sz@ = a pointer and length
+ *
+ * Returns:	---
+ *
+ * Use:		Ensures that the compiler generates code to compute @x@ or
+ *		the contents of the buffer at @p@.
+ */
+
+#ifndef ADMIRE
+#  define ADMIRE(x) ((void)(x))
+#endif
+#ifndef ADMIRE_BUF
+#  define ADMIRE_BUF(p, sz) ((void)(p), (void)(sz))
 #endif
 
-#ifndef PRINTF_LIKE
-#  define PRINF_LIKE(fmtix, argix)
+/* --- @RELAX@ --- *
+ *
+ * Arguments:	---
+ *
+ * Returns:	---
+ *
+ * Use:		Does nothing, but the compiler doesn't know that.
+ */
+
+#ifndef RELAX
+#  define RELAX
 #endif
 
-#ifndef SCANF_LIKE
-#  define SCANF_LIKE(fmtix, argix)
+/* --- @DEPRECATED@, @NORETURN@, @IGNORABLE@, @MUST_CHECK@ --- *
+ *
+ * Use:		These are (mostly) function attributes; write them among the
+ *		declaration specifiers for a function definition or
+ *		declaration.  These may not do anything, but the intended
+ *		behaviour is as follows.
+ *
+ *		  * @DEPRECATED(msg)@ -- report a warning, quoting the string
+ *		    literal @msg@, if the function is called.
+ *
+ *		  * @NORETURN@ -- promise that the function doesn't return to
+ *		    its caller: either it kills the process, or it performs
+ *		    some nonlocal transfer.
+ *
+ *		  * @IGNORABLE@ -- the item (which might be data rather than
+ *		    a function) might not be referred to, but that's OK:
+ *		    don't warn about it.
+ *
+ *		  @ @MUST_CHECK@ -- warn if the return value of a function is
+ *		    ignored.  Use @DISCARD@ if you really don't care.
+ */
+
+#ifndef DEPRECATED
+#  define DEPRECATED(msg)
 #endif
 
 #ifndef NORETURN
@@ -233,10 +456,94 @@
 #  define MUST_CHECK
 #endif
 
+/* --- @PRINTF_LIKE@, @SCANF_LIKE@, @EXECL_LIKE@ --- *
+ *
+ * Arguments:	@int fmtix@ = format string argument index (starting from 1)
+ *		@int argix@ = variable format argument tail index (starting
+ *			from 1)
+ *		@int ntrail@ = number of arguments following terminator
+ *
+ * Use:		These are function attributes.  Again, they might not do
+ *		anything at all.  By intention, they give the compiler
+ *		information about a variadic function's arguments, so that it
+ *		can warn about misuse.
+ *
+ *		  * @PRINTF_LIKE@ -- the function takes a @printf@-style
+ *		    format string as argument @fmtix@ and an argument tail
+ *		    (which may be empty) beginning with argument @argix@.
+ *
+ *		  * @SCANF_LIKE@ -- the function takes a @scanf@-style
+ *		    format string as argument @fmtix@ and an argument tail
+ *		    (which may be empty) beginning with argument @argix@.
+ *
+ *		  * @EXECL_LIKE@ -- the function takes a sequence of pointer
+ *		    arguments terminated by a null pointer, followed by
+ *		    @ntrail@ further arguments.
+ */
+
+#ifndef PRINTF_LIKE
+#  define PRINF_LIKE(fmtix, argix)
+#endif
+
+#ifndef SCANF_LIKE
+#  define SCANF_LIKE(fmtix, argix)
+#endif
+
+#ifndef EXECL_LIKE
+#  define EXECL_LIKE(ntrail)
+#endif
+
+/* --- @MUFFLE_WARNINGS_...@ --- *
+ *
+ * Arguments:	@warns@ = a sequence of @..._WARNING@ calls (see below)
+ *		@body@ = some program text
+ *
+ * Use:		Muffle specific warnings within the program text.
+ *
+ *		For @MUFFLE_WARNINGS_DECL@, the program text is a
+ *		declaration; for @MUFFLE_WARNINGS_EXPR@, it is an expression,
+ *		and for @MUFFLE_WARNINGS_STMT@, it is a statement.
+ *
+ *		The warnings to be muffled are given as a list of
+ *		@..._WARNING@ macros, with no separators.  The list can
+ *		list warnings from multiple different compilers: entries for
+ *		irrelevant compilers will be ignored.
+ */
+
+#ifndef MUFFLE_WARNINGS_DECL
+#  define MUFFLE_WARNINGS_DECL(warns, body) body
+#endif
+
+#ifndef MUFFLE_WARNINGS_EXPR
+#  define MUFFLE_WARNINGS_EXPR(warns, body) (body)
+#endif
+
+#ifndef MUFFLE_WARNINGS_STMT
+#  define MUFFLE_WARNINGS_STMT(warns, body) do { body } while (0)
+#endif
+
+/* --- @GCC_WARNING@ --- *
+ *
+ * Arguments:	@warn@ = a string literal naming a warning, with `%|-W...|%'
+ *			prefix
+ *
+ * Use:		Names a GCC warning: use within @MUFFLE_WARNINGS_...@.
+ *
+ *		Note that GCC's warning suppression is very buggy.
+ */
+
 #ifndef GCC_WARNING
 #  define GCC_WARNING(warn)
 #endif
 
+/* --- @CLANG_WARNING@ --- *
+ *
+ * Arguments:	@warn@ = a string literal naming a warning, with `%|-W...|%'
+ *			prefix
+ *
+ * Use:		Names a Clang warning: use within @MUFFLE_WARNINGS_...@.
+ */
+
 #ifndef CLANG_WARNING
 #  define CLANG_WARNING(warn)
 #endif