Fix bug in libzahl_msb_nz_* and optimise and simplify libzahl_realloc

Signed-off-by: Mattias Andrée <maandree@kth.se>

2 files changed, 11 insertions, 17 deletions

diff --git a/src/allocator.c b/src/allocator.c
index 7737046..80668f1 100644
--- a/src/allocator.c
+++ b/src/allocator.c
@@ -5,21 +5,15 @@
 void
 libzahl_realloc(z_t a, size_t need)
 {
-	size_t i, x;
+	size_t i, new_size = 1;
 	zahl_char_t *new;
 
-	/* Find n such that n is a minimal power of 2 ≥ need. */
-	if (likely((need & (~need + 1)) != need)) {
-		need |= need >> 1;
-		need |= need >> 2;
-		need |= need >> 4;
-		for (i = sizeof(need), x = 8; (i >>= 1); x <<= 1)
-			need |= need >> x;
-		need += 1;
+	new_size <<= i = libzahl_msb_nz_zu(need);
+	if (likely(new_size != need)) {
+		i += 1;
+		new_size <<= 1;
 	}
 
-	i = libzahl_msb_nz_zu(need);
-
 	if (likely(libzahl_pool_n[i])) {
 		libzahl_pool_n[i]--;
 		new = libzahl_pool[i][libzahl_pool_n[i]];
@@ -27,12 +21,12 @@ libzahl_realloc(z_t a, size_t need)
 		zfree(a);
 		a->chars = new;
 	} else {
-		a->chars = realloc(a->chars, need * sizeof(zahl_char_t));
+		a->chars = realloc(a->chars, new_size * sizeof(zahl_char_t));
 		if (unlikely(!a->chars)) {
 			if (!errno) /* sigh... */
 				errno = ENOMEM;
 			libzahl_failure(errno);
 		}
 	}
-	a->alloced = need;
+	a->alloced = new_size;
 }
diff --git a/src/internals.h b/src/internals.h
index da8ce0c..a9d9af5 100644
--- a/src/internals.h
+++ b/src/internals.h
@@ -150,15 +150,15 @@ zmemset(zahl_char_t *a, register zahl_char_t v, register size_t n)
 #endif
 
 #if defined(__GNUC__) || defined(__clang__)
-# define libzahl_msb_nz_lu(x)        (8 * sizeof(unsigned long int) - (size_t)__builtin_clzl(x));
-# define libzahl_msb_nz_llu(x)       (8 * sizeof(unsigned long long int) - (size_t)__builtin_clzll(x));
+# define libzahl_msb_nz_lu(x)        (8 * sizeof(unsigned long int) - 1 - (size_t)__builtin_clzl(x))
+# define libzahl_msb_nz_llu(x)       (8 * sizeof(unsigned long long int) - 1 - (size_t)__builtin_clzll(x))
 #else
 static inline size_t
 libzahl_msb_nz_lu(unsigned long int x)
 {
 	size_t r = 0;
 	for (; x; x >>= 1, r++);
-	return r;
+	return r - 1;
 }
 
 static inline size_t
@@ -166,7 +166,7 @@ libzahl_msb_nz_llu(unsigned long long int x)
 {
 	size_t r = 0;
 	for (; x; x >>= 1, r++);
-	return r;
+	return r - 1;
 }
 #endif