try to concatenate strings in-place when possible

2 files changed, 38 insertions, 18 deletions

diff --git a/arena.h b/arena.h
index 1be5cd7..5235204 100644
--- a/arena.h
+++ b/arena.h
@@ -24,6 +24,7 @@ void arena_free(Arena *a);
 void arena_reset(Arena *a);
 void *arena_alloc(Arena *a, size_t n, size_t align);
 void *arena_realloc(Arena *a, void *old, size_t oldsz, size_t newsz, size_t align);
+void *arena_concat(Arena *m, void *a, size_t asz, void *b, size_t bsz, size_t align);
 
 #define new(a, t)\
     memset(arena_alloc(a, sizeof(t), _Alignof(__typeof__(t))), 0, sizeof(t))
@@ -89,5 +90,15 @@ void *arena_realloc(Arena *a, void *old, size_t oldsz, size_t newsz, size_t alig
 	}
 }
 
+void *arena_concat(Arena *m, void *a, size_t asz, void *b, size_t bsz, size_t align) {
+	if (!asz)
+		return b;
+	if (!bsz || (char*)a + asz == b)
+		return a;
+	void *p = arena_realloc(m, a, asz, asz + bsz, align);
+	memcpy((char*)p + asz, b, bsz);
+	return p;
+}
+
 #endif
 #endif
diff --git a/str.h b/str.h
index b5f2889..1969d6b 100644
--- a/str.h
+++ b/str.h
@@ -17,36 +17,34 @@ typedef struct {
 
 #define S(s) (Str){s,sizeof(s)-1}
 
-char *str_to_cstr(Str s, Arena *a);
 Str str_from_cstr(const char *s);
+
 int str_eql(Str a, Str b);
 int str_starts(Str a, Str b);
 int str_ends(Str a, Str b);
-void str_catc(Str *a, char b, Arena *m);
+
 Str str_skip(Str a, ptrdiff_t n);
+Str str_trunc(Str a, ptrdiff_t n);
+
 Str str_trim_left(Str a);
 Str str_trim_right(Str a);
 Str str_trim(Str a);
+
 Cut str_cut(Str s, char c);
 Str str_findc(Str s, char c);
 Str str_find(Str haystack, Str needle);
 int str_contains(Str a, Str b);
-Str str_dup(Str a, Arena *m);
+
+char *str_to_cstr(Str s, Arena *a);
 void str_cat(Str *a, Str b, Arena *m);
+void str_catc(Str *a, char b, Arena *m);
+Str str_dup(Str a, Arena *m);
 Str str_replace_end(Str s, Str a, Str b, Arena *m);
 
 #ifdef STR_IMPL
 
 /* conversions */
 
-char *str_to_cstr(Str s, Arena *a) {
-	if (!s.n) return "";
-	char *r = new_arr(a, char, s.n + 1);
-	memcpy(r, s.s, s.n);
-	r[s.n] = 0;
-	return r;
-}
-
 Str str_from_cstr(const char *s) {
 	return (Str) { (char*)s, strlen(s) };
 }
@@ -65,15 +63,14 @@ int str_ends(Str a, Str b) {
 	return a.n >= b.n && !memcmp(&a.s[a.n - b.n], b.s, b.n);
 }
 
-void str_catc(Str *a, char b, Arena *m) {
-	a->s = resize(m, a->s, a->n, a->n + 1);
-	a->s[a->n++] = b;
-}
-
 Str str_skip(Str a, ptrdiff_t n) {
 	return (Str) { a.s + n, a.n - n };
 }
 
+Str str_trunc(Str a, ptrdiff_t n) {
+	return (Str) { a.s, n < a.n ? n : a.n };
+}
+
 static inline int str_is_space(char c) {
 	return c == ' ' || c == '\t' || c == '\n' || c == '\r';
 }
@@ -127,6 +124,14 @@ int str_contains(Str a, Str b) {
 
 /* allocating */
 
+char *str_to_cstr(Str s, Arena *a) {
+	if (!s.n) return "";
+	char *r = new_arr(a, char, s.n + 1);
+	memcpy(r, s.s, s.n);
+	r[s.n] = 0;
+	return r;
+}
+
 Str str_dup(Str a, Arena *m) {
 	char *s = new_arr(m, char, a.n);
 	memcpy(s, a.s, a.n);
@@ -135,11 +140,15 @@ Str str_dup(Str a, Arena *m) {
 }
 
 void str_cat(Str *a, Str b, Arena *m) {
-	a->s = resize(m, a->s, a->n, a->n + b.n);
-	memcpy(&a->s[a->n], b.s, b.n);
+	a->s = arena_concat(m, a->s, a->n, b.s, b.n, _Alignof(char));
 	a->n += b.n;
 }
 
+void str_catc(Str *a, char b, Arena *m) {
+	a->s = arena_concat(m, a->s, a->n, &b, 1, _Alignof(char));
+	a->n++;
+}
+
 Str str_replace_end(Str s, Str a, Str b, Arena *m) {
 	if (!str_ends(s, a)) return s;
 	char *p = new_arr(m, char, s.n + b.n - a.n);