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Better document binomial coefficents calculation

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This is just a first cut at that part of init code.

Verified new binomial coefficents are the same.

No functional change.
This commit is contained in:
Marco Costalba 2016-04-17 15:01:44 +02:00
parent f0650d499f
commit 230685d4ae
1 changed files with 17 additions and 44 deletions
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61
src/syzygy/tbcore.cpp
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@ -560,54 +560,27 @@ static int pfactor[5][4];
static void init_indices(void)
{
int i, j, k;
// There are Binomial(n, k) ways to choose k elements out of a set of n
// elements. Fill binomial[] with the binomial coefficents using pascal
// triangle algorithm so that binomial[k-1][n] = Binomial(n, k).
for (int k = 0; k < 5; k++)
{
binomial[k][0] = 0;
// binomial[k-1][n] = Bin(n, k)
for (i = 0; i < 5; i++)
for (j = 0; j < 64; j++) {
int f = j;
int l = 1;
for (int n = 1; n < 64; n++)
binomial[k][n] = (k ? binomial[k-1][n-1] : 1) + binomial[k][n-1];
}
for (k = 1; k <= i; k++) {
f *= (j - k);
l *= (k + 1);
}
binomial[i][j] = f / l;
}
for (i = 0; i < 5; i++) {
int s = 0;
for (j = 0; j < 6; j++) {
for (int s = 0, i = 0; i < 5; i++)
{
for (int j = 0; j < 24; j++)
{
pawnidx[i][j] = s;
s += (i == 0) ? 1 : binomial[i - 1][ptwist[invflap[j]]];
s += (i ? binomial[i - 1][ptwist[invflap[j]]] : 1);
if (j && !(j % 6))
pfactor[i][(j / 6) - 1] = s, s = 0;
}
pfactor[i][0] = s;
s = 0;
for (; j < 12; j++) {
pawnidx[i][j] = s;
s += (i == 0) ? 1 : binomial[i - 1][ptwist[invflap[j]]];
}
pfactor[i][1] = s;
s = 0;
for (; j < 18; j++) {
pawnidx[i][j] = s;
s += (i == 0) ? 1 : binomial[i - 1][ptwist[invflap[j]]];
}
pfactor[i][2] = s;
s = 0;
for (; j < 24; j++) {
pawnidx[i][j] = s;
s += (i == 0) ? 1 : binomial[i - 1][ptwist[invflap[j]]];
}
pfactor[i][3] = s;
}
}