Optimize kmod_elf_get_strings() by reducing calls to memcpy

Copy the entire string only once and then scan it, setting up the
pointers of the vector.

diff --git a/libkmod/libkmod-elf.c b/libkmod/libkmod-elf.c
index 2e8ab12..30feb76 100644 (file)
--- a/libkmod/libkmod-elf.c
+++ b/libkmod/libkmod-elf.c
@@ -395,11 +395,11 @@ static int kmod_elf_get_section(const struct kmod_elf *elf, const char *section,
 /* array will be allocated with strings in a single malloc, just free *array */
 int kmod_elf_get_strings(const struct kmod_elf *elf, const char *section, char ***array)
 {
-       uint64_t i, last, size;
+       size_t i, j, size, count;
        const void *buf;
        const char *strings;
-       char *itr, **a;
-       int count, err;
+       char *s, **a;
+       int err;
 
        *array = NULL;
 
@@ -434,33 +434,20 @@ int kmod_elf_get_strings(const struct kmod_elf *elf, const char *section, char *
        if (*array == NULL)
                return -errno;
 
+       s = (char *)(a + count + 1);
+       memcpy(s, strings, size);
+
+       /* make sure the last string is NULL-terminated */
+       s[size] = '\0';
        a[count] = NULL;
-       itr = (char *)(a + count);
-       last = 0;
+       a[0] = s;
 
-       for (i = 0, count = 0; i < size; i++) {
-               if (strings[i] == '\0') {
-                       size_t slen = i - last;
-                       if (last == i) {
-                               last = i + 1;
-                               continue;
-                       }
-                       a[count] = itr;
-                       memcpy(itr, strings + last, slen);
-                       itr[slen] = '\0';
-                       itr += slen + 1;
-                       count++;
-                       last = i + 1;
-               }
-       }
+       for (i = 0, j = 1; j < count && i < size; i++) {
+               if (s[i] != '\0')
+                       continue;
 
-       if (strings[i - 1] != '\0') {
-               size_t slen = i - last;
-               a[count] = itr;
-               memcpy(itr, strings + last, slen);
-               itr[slen] = '\0';
-               itr += slen + 1;
-               count++;
+               a[j] = &s[i + 1];
+               j++;
        }
 
        return count;