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libmp: avoid temporary buffer allocation in mprand()

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This commit is contained in:
cinap_lenrek 2016-12-28 18:19:52 +01:00
parent 7755561ae1
commit 45512020d2
1 changed files with 6 additions and 17 deletions
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23
sys/src/libmp/port/mprand.c
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@ -6,31 +6,20 @@ mpint*
mprand(int bits, void (*gen)(uchar*, int), mpint *b)
{
mpdigit mask;
int n, m;
uchar *p;
n = DIGITS(bits);
if(b == nil){
b = mpnew(bits);
setmalloctag(b, getcallerpc(&bits));
}else
mpbits(b, bits);
p = malloc(n*Dbytes);
if(p == nil)
sysfatal("mprand: %r");
(*gen)(p, n*Dbytes);
betomp(p, n*Dbytes, b);
free(p);
b->sign = 1;
b->top = DIGITS(bits);
(*gen)((uchar*)b->p, b->top*Dbytes);
// make sure we don't give too many bits
m = bits%Dbits;
if(m == 0)
return b;
mask = ((mpdigit)1 << (bits%Dbits))-1;
if(mask != 0)
b->p[b->top-1] &= mask;
mask = 1;
mask <<= m;
mask--;
b->p[n-1] &= mask;
return mpnorm(b);
}