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Small lookmapping nits:

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- remove bogus initialization using uninitialized i
- derive initial incr from hash
- copy mp->ma_table into a local variable
This commit is contained in:
Guido van Rossum 1997-01-29 15:53:56 +00:00
parent 5ed19dcc0e
commit efb4609c4a
2 changed files with 12 additions and 10 deletions
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11
Objects/dictobject.c
View file

@ -169,14 +169,15 @@ lookmapping(mp, key, hash)
register unsigned long sum = (unsigned long) hash; register unsigned long sum = (unsigned long) hash;
register mappingentry *freeslot = NULL; register mappingentry *freeslot = NULL;
register int mask = mp->ma_size-1; register int mask = mp->ma_size-1;
register mappingentry *ep = &mp->ma_table[i]; mappingentry *ep0 = mp->ma_table;
register mappingentry *ep;
/* We must come up with (i, incr) such that 0 <= i < 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 */ and 0 < incr < ma_size and both are a function of hash */
i = (~sum) & mask; i = (~sum) & mask;
/* We use ~sum instead if sum, as degenerate hash functions, such /* We use ~sum instead if sum, as degenerate hash functions, such
as for ints <sigh>, can have lots of leading zeros. It's not as for ints <sigh>, can have lots of leading zeros. It's not
really a performance risk, but better safe than sorry. */ really a performance risk, but better safe than sorry. */
ep = &mp->ma_table[i]; ep = &ep0[i];
if (ep->me_key == NULL) if (ep->me_key == NULL)
return ep; return ep;
if (ep->me_key == dummy) if (ep->me_key == dummy)
@ -185,16 +186,16 @@ lookmapping(mp, key, hash)
(ep->me_hash == hash && cmpobject(ep->me_key, key) == 0)) { (ep->me_hash == hash && cmpobject(ep->me_key, key) == 0)) {
return ep; return ep;
} }
/* Derive incr from i, just to make it more arbitrary. Note that /* Derive incr from sum, just to make it more arbitrary. Note that
incr must not be 0, or we will get into an infinite loop.*/ incr must not be 0, or we will get into an infinite loop.*/
incr = i << 1; incr = (sum ^ (sum >> 3)) & mask;
if (!incr) if (!incr)
incr = mask; incr = mask;
if (incr > mask) /* Cycle through GF(2^n)-{0} */ if (incr > mask) /* Cycle through GF(2^n)-{0} */
incr ^= mp->ma_poly; /* This will implicitly clear the incr ^= mp->ma_poly; /* This will implicitly clear the
highest bit */ highest bit */
for (;;) { for (;;) {
ep = &mp->ma_table[(i+incr)&mask]; ep = &ep0[(i+incr)&mask];
if (ep->me_key == NULL) { if (ep->me_key == NULL) {
if (freeslot != NULL) if (freeslot != NULL)
return freeslot; return freeslot;

11
Objects/mappingobject.c
View file

@ -169,14 +169,15 @@ lookmapping(mp, key, hash)
register unsigned long sum = (unsigned long) hash; register unsigned long sum = (unsigned long) hash;
register mappingentry *freeslot = NULL; register mappingentry *freeslot = NULL;
register int mask = mp->ma_size-1; register int mask = mp->ma_size-1;
register mappingentry *ep = &mp->ma_table[i]; mappingentry *ep0 = mp->ma_table;
register mappingentry *ep;
/* We must come up with (i, incr) such that 0 <= i < 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 */ and 0 < incr < ma_size and both are a function of hash */
i = (~sum) & mask; i = (~sum) & mask;
/* We use ~sum instead if sum, as degenerate hash functions, such /* We use ~sum instead if sum, as degenerate hash functions, such
as for ints <sigh>, can have lots of leading zeros. It's not as for ints <sigh>, can have lots of leading zeros. It's not
really a performance risk, but better safe than sorry. */ really a performance risk, but better safe than sorry. */
ep = &mp->ma_table[i]; ep = &ep0[i];
if (ep->me_key == NULL) if (ep->me_key == NULL)
return ep; return ep;
if (ep->me_key == dummy) if (ep->me_key == dummy)
@ -185,16 +186,16 @@ lookmapping(mp, key, hash)
(ep->me_hash == hash && cmpobject(ep->me_key, key) == 0)) { (ep->me_hash == hash && cmpobject(ep->me_key, key) == 0)) {
return ep; return ep;
} }
/* Derive incr from i, just to make it more arbitrary. Note that /* Derive incr from sum, just to make it more arbitrary. Note that
incr must not be 0, or we will get into an infinite loop.*/ incr must not be 0, or we will get into an infinite loop.*/
incr = i << 1; incr = (sum ^ (sum >> 3)) & mask;
if (!incr) if (!incr)
incr = mask; incr = mask;
if (incr > mask) /* Cycle through GF(2^n)-{0} */ if (incr > mask) /* Cycle through GF(2^n)-{0} */
incr ^= mp->ma_poly; /* This will implicitly clear the incr ^= mp->ma_poly; /* This will implicitly clear the
highest bit */ highest bit */
for (;;) { for (;;) {
ep = &mp->ma_table[(i+incr)&mask]; ep = &ep0[(i+incr)&mask];
if (ep->me_key == NULL) { if (ep->me_key == NULL) {
if (freeslot != NULL) if (freeslot != NULL)
return freeslot; return freeslot;