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New, better hash for floating point and complex

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This commit is contained in:
Guido van Rossum 1997-01-11 19:26:21 +00:00
parent 265b5b3f03
commit 919cf1aff1
2 changed files with 41 additions and 6 deletions
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36
Objects/complexobject.c
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@ -294,7 +294,7 @@ complex_hash(v)
{ {
double intpart, fractpart; double intpart, fractpart;
int expo; int expo;
long x; long hipart, x;
/* This is designed so that Python numbers with the same /* This is designed so that Python numbers with the same
value hash to the same value, otherwise comparisons value hash to the same value, otherwise comparisons
of mapping keys will turn out weird */ of mapping keys will turn out weird */
@ -309,7 +309,7 @@ complex_hash(v)
fractpart = modf(v->cval.real, &intpart); fractpart = modf(v->cval.real, &intpart);
#endif #endif
if (fractpart == 0.0) { if (fractpart == 0.0 && v->cval.imag == 0.0) {
if (intpart > 0x7fffffffL || -intpart > 0x7fffffffL) { if (intpart > 0x7fffffffL || -intpart > 0x7fffffffL) {
/* Convert to long int and use its hash... */ /* Convert to long int and use its hash... */
object *w = dnewlongobject(v->cval.real); object *w = dnewlongobject(v->cval.real);
@ -323,8 +323,36 @@ complex_hash(v)
} }
else { else {
fractpart = frexp(fractpart, &expo); fractpart = frexp(fractpart, &expo);
fractpart = fractpart*2147483648.0; /* 2**31 */ fractpart = fractpart * 2147483648.0; /* 2**31 */
x = (long) (intpart + fractpart) ^ expo; /* Rather arbitrary */ hipart = (long)fractpart; /* Take the top 32 bits */
fractpart = (fractpart - (double)hipart) * 2147483648.0;
/* Get the next 32 bits */
x = hipart + (long)fractpart + (long)intpart + (expo << 15);
/* Combine everything */
if (v->cval.imag != 0.0) { /* Hash the imaginary part */
/* XXX Note that this hashes complex(x, y)
to the same value as complex(y, x).
Still better than it used to be :-) */
#ifdef MPW
{
extended e;
fractpart = modf(v->cval.imag, &e);
intpart = e;
}
#else
fractpart = modf(v->cval.imag, &intpart);
#endif
fractpart = frexp(fractpart, &expo);
fractpart = fractpart * 2147483648.0; /* 2**31 */
hipart = (long)fractpart; /* Take the top 32 bits */
fractpart =
(fractpart - (double)hipart) * 2147483648.0;
/* Get the next 32 bits */
x ^= hipart + (long)fractpart +
(long)intpart + (expo << 15);
/* Combine everything */
}
} }
if (x == -1) if (x == -1)
x = -2; x = -2;

11
Objects/floatobject.c
View file

@ -236,9 +236,16 @@ float_hash(v)
x = (long)intpart; x = (long)intpart;
} }
else { else {
/* Note -- if you change this code, also change the copy
in complexobject.c */
long hipart;
fractpart = frexp(fractpart, &expo); fractpart = frexp(fractpart, &expo);
fractpart = fractpart*2147483648.0; /* 2**31 */ fractpart = fractpart * 2147483648.0; /* 2**31 */
x = (long) (intpart + fractpart) ^ expo; /* Rather arbitrary */ hipart = (long)fractpart; /* Take the top 32 bits */
fractpart = (fractpart - (double)hipart) * 2147483648.0;
/* Get the next 32 bits */
x = hipart + (long)fractpart + (long)intpart + (expo << 15);
/* Combine everything */
} }
if (x == -1) if (x == -1)
x = -2; x = -2;