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update the zipmap entry in-place instead of appending it

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Pieter Noordhuis 2010-04-01 14:02:22 +02:00
parent bfded2aa51
commit da2cfe8a3b
1 changed files with 20 additions and 13 deletions
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33
zipmap.c
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@ -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;