mem: Add memswap() function

Add a memswap() function to the mem module, which exchanges two (equal
sized, non-overlapping) memory regions.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

diff --git a/ccan/mem/mem.c b/ccan/mem/mem.c
index 91c9961a52ecd92d1372dae98b07f54902e25f22..5b4b3508090dfb10dc7eea9236eb42ed54b92834 100644 (file)
--- a/ccan/mem/mem.c
+++ b/ccan/mem/mem.c
@@ -2,6 +2,7 @@
 
 #include "config.h"
 
+#include <assert.h>
 #include <string.h>
 #include <ccan/mem/mem.h>
 
@@ -64,3 +65,26 @@ void *memcchr(void const *data, int c, size_t data_len)
 
        return NULL;
 }
+
+#define MEMSWAP_TMP_SIZE       256
+
+void memswap(void *a, void *b, size_t n)
+{
+       char *ap = a;
+       char *bp = b;
+       char tmp[MEMSWAP_TMP_SIZE];
+
+       assert(!memoverlaps(a, n, b, n));
+
+       while (n) {
+               size_t m = n > MEMSWAP_TMP_SIZE ? MEMSWAP_TMP_SIZE : n;
+
+               memcpy(tmp, bp, m);
+               memcpy(bp, ap, m);
+               memcpy(ap, tmp, m);
+
+               ap += m;
+               bp += m;
+               n -= m;
+       }
+}

diff --git a/ccan/mem/mem.h b/ccan/mem/mem.h
index 99c34c0a39719ec0a262add21e74bab5b99a8e56..dd66cc62cd8cce990aeac17da41962aa2bf74a74 100644 (file)
--- a/ccan/mem/mem.h
+++ b/ccan/mem/mem.h
@@ -217,4 +217,14 @@ static inline bool memoverlaps(const void *a_, size_t al,
        return (a < (b + bl)) && (b < (a + al));
 }
 
+/*
+ * memswap - Exchange two memory regions
+ * @a: first region
+ * @b: second region
+ * @n: length of the regions
+ *
+ * Undefined results if the two memory regions overlap.
+ */
+void memswap(void *a, void *b, size_t n);
+
 #endif /* CCAN_MEM_H */

diff --git a/ccan/mem/test/api.c b/ccan/mem/test/api.c
index a584c0f33e3b97a11974e55e51670991db4a6bdd..d820a38ddf35bd9ed68097d681ebf02bb8de40e0 100644 (file)
--- a/ccan/mem/test/api.c
+++ b/ccan/mem/test/api.c
@@ -1,6 +1,12 @@
+#include "config.h"
+
+#include <assert.h>
+
 #include <ccan/mem/mem.h>
 #include <ccan/tap/tap.h>
 
+#define SWAPSIZE       12
+
 int main(void)
 {
        char haystack1[] = "abcd\0efgh";
@@ -9,9 +15,10 @@ int main(void)
        char needle2[] = "d\0e";
        char scan1[] = "aaaab";
        char scan2[] = "\0\0\0b";
+       char tmp1[SWAPSIZE], tmp2[SWAPSIZE];
 
        /* This is how many tests you plan to run */
-       plan_tests(60);
+       plan_tests(62);
 
        ok1(memmem(haystack1, sizeof(haystack1), needle1, 2) == haystack1);
        ok1(memmem(haystack1, sizeof(haystack1), needle1, 3) == NULL);
@@ -96,6 +103,16 @@ int main(void)
        ok1(memoverlaps(haystack1 + 4, 7, haystack1, 5));
        ok1(!memoverlaps(haystack1 + 5, 6, haystack1, 5));
 
+       assert(sizeof(haystack1) <= SWAPSIZE);
+       assert(sizeof(haystack2) <= SWAPSIZE);
+       memset(tmp1, 0, sizeof(tmp1));
+       memset(tmp2, 0, sizeof(tmp2));
+       memcpy(tmp1, haystack1, sizeof(haystack1));
+       memcpy(tmp2, haystack2, sizeof(haystack2));
+       memswap(tmp1, tmp2, SWAPSIZE);
+       ok1(memcmp(tmp1, haystack2, sizeof(haystack2)) == 0);
+       ok1(memcmp(tmp2, haystack1, sizeof(haystack1)) == 0);
+
        /* This exits depending on whether all tests passed */
        return exit_status();
 }