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Rewrote lookmapping() according to suggestions by Jyrki Alakuijala.

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This commit is contained in:
Guido van Rossum 1997-01-16 21:06:45 +00:00
parent 3b039faf19
commit 7d18159614
2 changed files with 144 additions and 44 deletions
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94
Objects/dictobject.c
View file

@ -129,38 +129,88 @@ is a prime number). My choice for incr is somewhat arbitrary.
static mappingentry *lookmapping PROTO((mappingobject *, object *, long));
static mappingentry *
lookmapping(mp, key, hash)
register mappingobject *mp;
mappingobject *mp;
object *key;
long hash;
{
register int i, incr;
register unsigned long sum = (unsigned long) hash;
register mappingentry *freeslot = NULL;
register int size = mp->ma_size;
/* We must come up with (i, incr) such that 0 <= i < ma_size
and 0 < incr < ma_size and both are a function of hash */
i = sum % size;
/* Optimizations based on observations by Jyrki Alakuijala
(paraphrased):
- This routine is very heavily used, so should be AFAP
(As Fast As Possible).
- Most of the time, the first try is a hit or a definite
miss; so postpone the calculation of incr until we know the
first try was a miss.
- Write the loop twice, so we can move the test for
freeslot==NULL out of the loop.
- Write the loop using pointer increments and comparisons
rather than using an integer loop index.
Note that it behooves the compiler to calculate the values
of incr*sizeof(*ep) outside the loops and use this in the
increment of ep. I've reduced the number of register
variables to the two most obvious candidates.
*/
register mappingentry *ep;
mappingentry *end;
register object *ekey;
mappingentry *freeslot;
unsigned long sum;
int incr;
int size;
ep = &mp->ma_table[(unsigned long)hash%mp->ma_size];
ekey = ep->me_key;
if (ekey == NULL)
return ep;
if (ekey == dummy)
freeslot = ep;
else if (ep->me_hash == hash && cmpobject(ekey, key) == 0)
return ep;
else
freeslot = NULL;
size = mp->ma_size;
sum = hash;
do {
sum = 3*sum + 1;
incr = sum % size;
} while (incr == 0);
for (;;) {
register mappingentry *ep = &mp->ma_table[i];
if (ep->me_key == NULL) {
if (freeslot != NULL)
return freeslot;
else
end = mp->ma_table + size;
if (freeslot == NULL) {
for (;;) {
ep += incr;
if (ep >= end)
ep -= size;
ekey = ep->me_key;
if (ekey == NULL)
return ep;
if (ekey == dummy) {
freeslot = ep;
break;
}
if (ep->me_hash == hash && cmpobject(ekey, key) == 0)
return ep;
}
if (ep->me_key == dummy) {
if (freeslot == NULL)
freeslot = ep;
}
else if (ep->me_hash == hash &&
cmpobject(ep->me_key, key) == 0) {
}
for (;;) {
ep += incr;
if (ep >= end)
ep -= size;
ekey = ep->me_key;
if (ekey == NULL)
return freeslot;
if (ekey != dummy &&
ep->me_hash == hash && cmpobject(ekey, key) == 0)
return ep;
}
i = (i + incr) % size;
}
}

94
Objects/mappingobject.c
View file

@ -129,38 +129,88 @@ is a prime number). My choice for incr is somewhat arbitrary.
static mappingentry *lookmapping PROTO((mappingobject *, object *, long));
static mappingentry *
lookmapping(mp, key, hash)
register mappingobject *mp;
mappingobject *mp;
object *key;
long hash;
{
register int i, incr;
register unsigned long sum = (unsigned long) hash;
register mappingentry *freeslot = NULL;
register int size = mp->ma_size;
/* We must come up with (i, incr) such that 0 <= i < ma_size
and 0 < incr < ma_size and both are a function of hash */
i = sum % size;
/* Optimizations based on observations by Jyrki Alakuijala
(paraphrased):
- This routine is very heavily used, so should be AFAP
(As Fast As Possible).
- Most of the time, the first try is a hit or a definite
miss; so postpone the calculation of incr until we know the
first try was a miss.
- Write the loop twice, so we can move the test for
freeslot==NULL out of the loop.
- Write the loop using pointer increments and comparisons
rather than using an integer loop index.
Note that it behooves the compiler to calculate the values
of incr*sizeof(*ep) outside the loops and use this in the
increment of ep. I've reduced the number of register
variables to the two most obvious candidates.
*/
register mappingentry *ep;
mappingentry *end;
register object *ekey;
mappingentry *freeslot;
unsigned long sum;
int incr;
int size;
ep = &mp->ma_table[(unsigned long)hash%mp->ma_size];
ekey = ep->me_key;
if (ekey == NULL)
return ep;
if (ekey == dummy)
freeslot = ep;
else if (ep->me_hash == hash && cmpobject(ekey, key) == 0)
return ep;
else
freeslot = NULL;
size = mp->ma_size;
sum = hash;
do {
sum = 3*sum + 1;
incr = sum % size;
} while (incr == 0);
for (;;) {
register mappingentry *ep = &mp->ma_table[i];
if (ep->me_key == NULL) {
if (freeslot != NULL)
return freeslot;
else
end = mp->ma_table + size;
if (freeslot == NULL) {
for (;;) {
ep += incr;
if (ep >= end)
ep -= size;
ekey = ep->me_key;
if (ekey == NULL)
return ep;
if (ekey == dummy) {
freeslot = ep;
break;
}
if (ep->me_hash == hash && cmpobject(ekey, key) == 0)
return ep;
}
if (ep->me_key == dummy) {
if (freeslot == NULL)
freeslot = ep;
}
else if (ep->me_hash == hash &&
cmpobject(ep->me_key, key) == 0) {
}
for (;;) {
ep += incr;
if (ep >= end)
ep -= size;
ekey = ep->me_key;
if (ekey == NULL)
return freeslot;
if (ekey != dummy &&
ep->me_hash == hash && cmpobject(ekey, key) == 0)
return ep;
}
i = (i + incr) % size;
}
}