Add bt_common_sep_digits()

[babeltrace.git] / src / common / common.c

diff --git a/src/common/common.c b/src/common/common.c
index a81f8e79acd7a9a86de1fb271fb6c2f2af3374fe..4aa8fcd2a70e3ec9a890182fbf7f89350c97936f 100644 (file)
--- a/src/common/common.c
+++ b/src/common/common.c
@@ -1567,3 +1567,106 @@ void bt_common_custom_snprintf(char *buf, size_t buf_size,
                priv_data, fmt, &args);
        va_end(args);
 }
+
+BT_HIDDEN
+void bt_common_sep_digits(char *str, unsigned int digits_per_group, char sep)
+{
+       const char *rd;
+       char *wr;
+       uint64_t i = 0;
+       uint64_t orig_len;
+       uint64_t sep_count;
+       uint64_t new_len;
+
+       BT_ASSERT(digits_per_group > 0);
+       BT_ASSERT(sep != '\0');
+
+       /* Compute new length of `str` */
+       orig_len = strlen(str);
+       BT_ASSERT(orig_len > 0);
+       sep_count = (orig_len - 1) / digits_per_group;
+       new_len = strlen(str) + sep_count;
+
+       /*
+        * Do the work in place. Have the reading pointer `rd` start at
+        * the end of the original string, and the writing pointer `wr`
+        * start at the end of the new string, making sure to also put a
+        * null character there.
+        */
+       rd = str + orig_len - 1;
+       wr = str + new_len;
+       *wr = '\0';
+       wr--;
+
+       /*
+        * Here's what the process looks like (3 digits per group):
+        *
+        *     Source:      12345678
+        *                         ^
+        *     Destination: 12345678#8
+        *                           ^
+        *
+        *     Source:      12345678
+        *                        ^
+        *     Destination: 1234567878
+        *                          ^
+        *
+        *     Source:      12345678
+        *                       ^
+        *     Destination: 1234567678
+        *                         ^
+        *
+        *     Source:      12345678
+        *                      ^
+        *     Destination: 123456,678
+        *                        ^
+        *
+        *     Source:      12345678
+        *                      ^
+        *     Destination: 123455,678
+        *                       ^
+        *
+        *     Source:      12345678
+        *                     ^
+        *     Destination: 123445,678
+        *                      ^
+        *
+        *     Source:      12345678
+        *                    ^
+        *     Destination: 123345,678
+        *                     ^
+        *
+        *     Source:      12345678
+        *                   ^
+        *     Destination: 12,345,678
+        *                    ^
+        *
+        *     Source:      12345678
+        *                   ^
+        *     Destination: 12,345,678
+        *                   ^
+        *
+        *     Source:      12345678
+        *                  ^
+        *     Destination: 12,345,678
+        *                  ^
+        */
+       while (rd != str - 1) {
+               if (i == digits_per_group) {
+                       /*
+                        * Time to append the separator: decrement `wr`,
+                        * but keep `rd` as is.
+                        */
+                       i = 0;
+                       *wr = sep;
+                       wr--;
+                       continue;
+               }
+
+               /* Copy read-side character to write-side character */
+               *wr = *rd;
+               wr--;
+               rd--;
+               i++;
+       }
+}