implement "low hanging fruit" from C11

based on Gregor's patch sent to the list. includes:
- stdalign.h
- removing gets in C11 mode
- adding aligned_alloc and adjusting other functions to use it
- adding 'x' flag to fopen for exclusive mode

include/stdalign.h

+#ifndef _STDALIGN_H
+#define _STDALIGN_H
+
+/* this whole header only works in C11 or with compiler extensions */
+#if __STDC_VERSION__ < 201112L && defined( __GNUC__)
+#define _Alignas(t) __attribute__((__aligned__(t)))
+#define _Alignof(t) __alignof__(t)
+#endif
+
+#define alignas _Alignas
+#define alignof _Alignof
+#define __alignas_is_defined 1
+#define __alignof_is_defined 1
+
+#endif

include/stdio.h

@@ -90,7 +90,9 @@ int putc(int, FILE *);
 int putchar(int);
 
 char *fgets(char *, int, FILE *);
+#if __STDC_VERSION__ < 201112L
 char *gets(char *);
+#endif
 
 int fputs(const char *, FILE *);
 int puts(const char *);

include/stdlib.h

@@ -38,6 +38,7 @@ void *malloc (size_t);
 void *calloc (size_t, size_t);
 void *realloc (void *, size_t);
 void free (void *);
+void *aligned_alloc(size_t alignment, size_t size);
 
 void abort (void);
 int atexit (void (*) (void));

src/malloc/aligned_alloc.c

+#include <stdlib.h>
+#include <stdint.h>
+#include <errno.h>
+
+/* This function should work with most dlmalloc-like chunk bookkeeping
+ * systems, but it's only guaranteed to work with the native implementation
+ * used in this library. */
+
+void *aligned_alloc(size_t align, size_t len)
+{
+	unsigned char *mem, *new, *end;
+	size_t header, footer;
+
+	if ((align & -align & -sizeof(void *)) != align) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	if (len > SIZE_MAX - align) {
+		errno = ENOMEM;
+		return NULL;
+	}
+
+	if (align <= 4*sizeof(size_t)) {
+		if (!(mem = malloc(len)))
+			return NULL;
+		return mem;
+	}
+
+	if (!(mem = malloc(len + align-1)))
+		return NULL;
+
+	header = ((size_t *)mem)[-1];
+	end = mem + (header & -8);
+	footer = ((size_t *)end)[-2];
+	new = (void *)((uintptr_t)mem + align-1 & -align);
+
+	if (!(header & 7)) {
+		((size_t *)new)[-2] = ((size_t *)mem)[-2] + (new-mem);
+		((size_t *)new)[-1] = ((size_t *)mem)[-1] - (new-mem);
+		return new;
+	}
+
+	((size_t *)mem)[-1] = header&7 | new-mem;
+	((size_t *)new)[-2] = footer&7 | new-mem;
+	((size_t *)new)[-1] = header&7 | end-new;
+	((size_t *)end)[-2] = footer&7 | end-new;
+
+	if (new != mem) free(mem);
+	return new;
+}

src/malloc/memalign.c

@@ -3,11 +3,5 @@
 
 void *memalign(size_t align, size_t len)
 {
-	void *mem;
-	int ret;
-	if ((ret = posix_memalign(&mem, align, len))) {
-		errno = ret;
-		return 0;
-	}
-	return mem;
+	return aligned_alloc(align, len);
 }

src/malloc/posix_memalign.c

 #include <stdlib.h>
-#include <stdint.h>
 #include <errno.h>
 
-/* This function should work with most dlmalloc-like chunk bookkeeping
- * systems, but it's only guaranteed to work with the native implementation
- * used in this library. */
-
 int posix_memalign(void **res, size_t align, size_t len)
 {
-	unsigned char *mem, *new, *end;
-	size_t header, footer;
-
-	if ((align & -align & -sizeof(void *)) != align) return EINVAL;
-	if (len > SIZE_MAX - align) return ENOMEM;
-
-	if (align <= 4*sizeof(size_t)) {
-		if (!(mem = malloc(len)))
-			return errno;
-		*res = mem;
-		return 0;
-	}
-
-	if (!(mem = malloc(len + align-1)))
-		return errno;
-
-	header = ((size_t *)mem)[-1];
-	end = mem + (header & -8);
-	footer = ((size_t *)end)[-2];
-	new = (void *)((uintptr_t)mem + align-1 & -align);
-
-	if (!(header & 7)) {
-		((size_t *)new)[-2] = ((size_t *)mem)[-2] + (new-mem);
-		((size_t *)new)[-1] = ((size_t *)mem)[-1] - (new-mem);
-		*res = new;
-		return 0;
-	}
-
-	((size_t *)mem)[-1] = header&7 | new-mem;
-	((size_t *)new)[-2] = footer&7 | new-mem;
-	((size_t *)new)[-1] = header&7 | end-new;
-	((size_t *)end)[-2] = footer&7 | end-new;
-
-	if (new != mem) free(mem);
-	*res = new;
+	void *mem = aligned_alloc(align, len);
+	if (!mem) return errno;
+	*res = mem;
 	return 0;
 }

src/stdio/fopen.c

@@ -5,7 +5,6 @@ FILE *fopen(const char *filename, const char *mode)
 	FILE *f;
 	int fd;
 	int flags;
-	int plus = !!strchr(mode, '+');
 
 	/* Check for valid initial mode character */
 	if (!strchr("rwa", *mode)) {
@@ -14,9 +13,10 @@ FILE *fopen(const char *filename, const char *mode)
 	}
 
 	/* Compute the flags to pass to open() */
-	if (plus) flags = O_RDWR;
+	if (strchr(mode, '+')) flags = O_RDWR;
 	else if (*mode == 'r') flags = O_RDONLY;
 	else flags = O_WRONLY;
+	if (strchr(mode, 'x')) flags |= O_EXCL;
 	if (*mode != 'r') flags |= O_CREAT;
 	if (*mode == 'w') flags |= O_TRUNC;
 	if (*mode == 'a') flags |= O_APPEND;