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New long_lshift, without restriction on size of shift count, by Tim Peters. 

This makes it possible to write 1L<<1000000, memory permitting.
This commit is contained in:
Guido van Rossum 1997-03-16 00:37:59 +00:00
parent e053c67780
commit f2e499b1d7
1 changed files with 21 additions and 25 deletions
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46
Objects/longobject.c
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@ -1214,10 +1214,11 @@ long_lshift(a, b)
longobject *a;
longobject *b;
{
/* This version due to Tim Peters */
longobject *z;
long shiftby;
int newsize, wordshift, loshift, hishift, i, j;
digit lomask, himask;
int oldsize, newsize, wordshift, remshift, i, j;
twodigits accum;
shiftby = getlongvalue((object *)b);
if (shiftby == -1L && err_occurred())
@ -1226,26 +1227,18 @@ long_lshift(a, b)
err_setstr(ValueError, "negative shift count");
return NULL;
}
if (shiftby > MASK) {
if ((long)(int)shiftby != shiftby) {
err_setstr(ValueError, "outrageous left shift count");
return NULL;
}
if (shiftby % SHIFT == 0) {
wordshift = shiftby / SHIFT;
loshift = 0;
hishift = SHIFT;
newsize = ABS(a->ob_size) + wordshift;
lomask = MASK;
himask = 0;
}
else {
wordshift = shiftby / SHIFT + 1;
loshift = SHIFT - shiftby%SHIFT;
hishift = shiftby % SHIFT;
newsize = ABS(a->ob_size) + wordshift;
lomask = ((digit)1 << hishift) - 1;
himask = MASK ^ lomask;
}
/* wordshift, remshift = divmod(shiftby, SHIFT) */
wordshift = (int)shiftby / SHIFT;
remshift = (int)shiftby - wordshift * SHIFT;
oldsize = ABS(a->ob_size);
newsize = oldsize + wordshift;
if (remshift)
++newsize;
z = alloclongobject(newsize);
if (z == NULL)
return NULL;
@ -1253,13 +1246,16 @@ long_lshift(a, b)
z->ob_size = -(z->ob_size);
for (i = 0; i < wordshift; i++)
z->ob_digit[i] = 0;
for (i = wordshift, j = 0; i < newsize; i++, j++) {
if (i > 0)
z->ob_digit[i-1] |=
(a->ob_digit[j] << hishift) & himask;
z->ob_digit[i] =
(a->ob_digit[j] >> loshift) & lomask;
accum = 0;
for (i = wordshift, j = 0; j < oldsize; i++, j++) {
accum |= a->ob_digit[j] << remshift;
z->ob_digit[i] = (digit)(accum & MASK);
accum >>= SHIFT;
}
if (remshift)
z->ob_digit[newsize-1] = (digit)accum;
else
assert(!accum);
return (object *) long_normalize(z);
}