+
+struct substring
+replace_string (struct expression *e,
+ struct substring haystack,
+ struct substring needle,
+ struct substring replacement,
+ double n)
+{
+ if (!needle.length
+ || haystack.length < needle.length
+ || n <= 0
+ || n == SYSMIS)
+ return haystack;
+
+ struct substring result = alloc_string (e, MAX_STRING);
+ result.length = 0;
+
+ size_t i = 0;
+ while (i <= haystack.length - needle.length)
+ if (!memcmp (&haystack.string[i], needle.string, needle.length))
+ {
+ size_t copy_len = MIN (replacement.length, MAX_STRING - result.length);
+ memcpy (&result.string[result.length], replacement.string, copy_len);
+ result.length += copy_len;
+ i += needle.length;
+
+ if (--n < 1)
+ break;
+ }
+ else
+ {
+ if (result.length < MAX_STRING)
+ result.string[result.length++] = haystack.string[i];
+ i++;
+ }
+ while (i < haystack.length && result.length < MAX_STRING)
+ result.string[result.length++] = haystack.string[i++];
+
+ return result;
+}