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pc: add rev function

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This commit is contained in:
aiju 2016-08-31 13:00:50 +00:00
parent e95082f66c
commit 560ea5474c
2 changed files with 36 additions and 0 deletions
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3
sys/man/1/pc
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@ -84,6 +84,9 @@ Numbers exactly halfway between are rounded to the next even multiple.
.I xtend(n,m)
\fIn\fR truncated to \fIm\fR bits, with the highest bit interpreted as a sign bit.
.TP
.I rev(n,m)
\fIn\fR truncated to \fIm\fR bits, with the order of bits reversed.
.TP
.I ubits(n)
The minimum number of bits required to represent \fIn\fR as an unsigned number.
.TP

33
sys/src/cmd/pc.y
View file

@ -804,6 +804,38 @@ fnminv(int, Num **a)
return a[0];
}
Num *
fnrev(int, Num **a)
{
mpdigit v, m;
int i, j, n;
if(toint(a[1], &n, 1)){
numdecref(a[0]);
numdecref(a[1]);
return nil;
}
a[0] = nummod(a[0]);
mptrunc(a[0], n, a[0]);
for(i = 0; i < a[0]->top; i++){
v = a[0]->p[i];
m = -1;
for(j = sizeof(mpdigit) * 8; j >>= 1; ){
m ^= m << j;
v = v >> j & m | v << j & ~m;
}
a[0]->p[i] = v;
}
for(i = 0; i < a[0]->top / 2; i++){
v = a[0]->p[i];
a[0]->p[i] = a[0]->p[a[0]->top - 1 - i];
a[0]->p[a[0]->top - 1 - i] = v;
}
mpleft(a[0], n - a[0]->top * sizeof(mpdigit) * 8, a[0]);
numdecref(a[1]);
return a[0];
}
void
main(int argc, char **argv)
{
@ -830,6 +862,7 @@ main(int argc, char **argv)
regfunc("gcd", fngcd, 2);
regfunc("minv", fnminv, 2);
regfunc("rand", fnrand, 1);
regfunc("rev", fnrev, 2);
prompt = 1;
ARGBEGIN{