add numerical recipes library

lib/nr/cpp/recipes/mpmul.cpp

@@ -0,0 +1,38 @@
+#include "nr.h"
+
+void NR::mpmul(Vec_O_UCHR &w, Vec_I_UCHR &u, Vec_I_UCHR &v)
+{
+	const DP RX=256.0;
+	int j,n_max,nn=1;
+	DP cy,t;
+
+	int n=u.size();
+	int m=v.size();
+	int p=w.size();
+	n_max=MAX(m,n);
+	while (nn < n_max) nn <<= 1;
+	nn <<= 1;
+	Vec_DP a(0.0,nn),b(0.0,nn);
+	for (j=0;j<n;j++) a[j]=u[j];
+	for (j=0;j<m;j++) b[j]=v[j];
+	realft(a,1);
+	realft(b,1);
+	b[0] *= a[0];
+	b[1] *= a[1];
+	for (j=2;j<nn;j+=2) {
+		b[j]=(t=b[j])*a[j]-b[j+1]*a[j+1];
+		b[j+1]=t*a[j+1]+b[j+1]*a[j];
+	}
+	realft(b,-1);
+	cy=0.0;
+	for (j=nn-1;j>=0;j--) {
+		t=b[j]/(nn >> 1)+cy+0.5;
+		cy=(unsigned long) (t/RX);
+		b[j]=t-cy*RX;
+	}
+	if (cy >= RX) nrerror("cannot happen in mpmul");
+	for (j=0;j<p;j++) w[j]=0;
+	w[0]=(unsigned char) cy;
+	for (j=1;j<MIN(n+m,p);j++)
+		w[j]=(unsigned char) b[j-1];
+}