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update the zipmap entry in-place instead of appending it

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commit da2cfe8a3baeaad619c11290acf377f4ea7356c1 1 parent bfded2a
@pietern pietern authored
Showing with 20 additions and 13 deletions.
  1. +20 −13 zipmap.c
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33 zipmap.c
@@ -208,7 +208,7 @@ static inline unsigned char *zipmapResize(unsigned char *zm, unsigned int len) {
* If 'update' is not NULL, *update is set to 1 if the key was
* already preset, otherwise to 0. */
unsigned char *zipmapSet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned char *val, unsigned int vlen, int *update) {
- unsigned int zmlen;
+ unsigned int zmlen, offset;
unsigned int freelen, reqlen = zipmapRequiredLength(klen,vlen);
unsigned int empty, vempty;
unsigned char *p;
@@ -230,27 +230,34 @@ unsigned char *zipmapSet(unsigned char *zm, unsigned char *key, unsigned int kle
if (update) *update = 1;
freelen = zipmapRawEntryLength(p);
if (freelen < reqlen) {
- /* Move remaining entries to the current position, so this
- * pair can be appended. Note: the +1 in memmove is caused
- * by the end-of-zipmap byte. */
- memmove(p, p+freelen, zmlen-((p-zm)+freelen+1));
+ /* Store the offset of this key within the current zipmap, so
+ * it can be resized. Then, move the tail backwards so this
+ * pair fits at the current position. */
+ offset = p-zm;
zm = zipmapResize(zm, zmlen-freelen+reqlen);
- p = zm+zmlen-1-freelen;
- zmlen = zmlen-1-freelen+reqlen;
+ p = zm+offset;
+
+ /* The +1 in the number of bytes to be moved is caused by the
+ * end-of-zipmap byte. Note: the *original* zmlen is used. */
+ memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1));
+ zmlen = zmlen-freelen+reqlen;
freelen = reqlen;
}
}
- /* Ok we have a suitable block where to write the new key/value
- * entry. */
+ /* We now have a suitable block where the key/value entry can
+ * be written. If there is too much free space, move the tail
+ * of the zipmap a few bytes to the front and shrink the zipmap,
+ * as we want zipmaps to be very space efficient. */
empty = freelen-reqlen;
- /* If there is too much free space mark it as a free block instead
- * of adding it as trailing empty space for the value, as we want
- * zipmaps to be very space efficient. */
if (empty >= ZIPMAP_VALUE_MAX_FREE) {
- memmove(p+reqlen, p+freelen, zmlen-((p-zm)+freelen+1));
+ /* First, move the tail <empty> bytes to the front, then resize
+ * the zipmap to be <empty> bytes smaller. */
+ offset = p-zm;
+ memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1));
zmlen -= empty;
zm = zipmapResize(zm, zmlen);
+ p = zm+offset;
vempty = 0;
} else {
vempty = empty;
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