IMPROVES-i12 split cmp11sht.c into lib11sht.{c,h}

lib11sht.h

@@ -0,0 +1,39 @@
+/* ************************************************************************ *
+ *    lib11sht.h, v1.0                                                      *
+ *    Fuzzy comparison library: public API                                  *
+ *                                                                          *
+ *    Copyright (C) 2025 by Ruben Carlo Benante <rcb@beco.cc>               *
+ *    GNU GPL version 2 or later.                                           *
+ * ************************************************************************ */
+
+#ifndef LIB11SHT_H
+#define LIB11SHT_H
+
+#define LEVN_SBUFF 256  /* min size for s1/s2 buffers and bounded input */
+
+/* Compare similarity between two strings (after asciify + trim + lowercase).
+ * Returns:
+ *      0  if equal or similar above the given threshold ratio
+ *     -1  if a < b alphabetically (after normalization)
+ *     +1  if a > b alphabetically (after normalization)
+ * On error: sets errno = EINVAL and returns 0; comparison result is undefined.
+ * Caller must reset errno = 0 before the call to detect errors.
+ *
+ * Parameters:
+ *   a, b   input strings (NUL-terminated, may contain UTF-8 accented Latin chars)
+ *   thr    Levenshtein similarity threshold 0.0..1.0; matches above this count as equal
+ *   ratio  out: Levenshtein similarity 0.0..1.0 (1.0 on exact-after-normalize)
+ *   s1, s2 out: caller-provided buffers (>= LEVN_SBUFF) filled with the
+ *          normalized inputs (useful for diagnostics; can be ignored)
+ */
+int sequal(char *a, char *b, float thr, float *ratio, char *s1, char *s2);
+
+/* Compare two floats within ±delta.
+ * Returns:
+ *      0  if |a - b| <= delta
+ *     -1  if a < b - delta
+ *     +1  if a > b + delta
+ */
+int fequal(float a, float b, float delta);
+
+#endif /* LIB11SHT_H */