add numerical recipes library

lib/nr/cpp/recipes/icrc.cpp

@@ -0,0 +1,41 @@
+#include "nr.h"
+
+namespace {
+	inline unsigned char lobyte(const unsigned short x)
+	{
+		return (unsigned char)((x) & 0xff);
+	}
+
+	inline unsigned char hibyte(const unsigned short x)
+	{
+		return (unsigned char)((x >> 8) & 0xff);
+	}
+}
+
+unsigned short NR::icrc(const unsigned short crc, const string &bufptr,
+	const short jinit, const int jrev)
+{
+	static unsigned short icrctb[256],init=0;
+	static unsigned char rchr[256];
+	unsigned short j,cword=crc;
+	static unsigned char it[16]={0,8,4,12,2,10,6,14,1,9,5,13,3,11,7,15};
+
+	unsigned long len=bufptr.length();
+	if (init == 0) {
+		init=1;
+		for (j=0;j<256;j++) {
+			icrctb[j]=icrc1(j << 8,0);
+			rchr[j]=(unsigned char)((it[j & 0xf] << 4) | (it[j >> 4]));
+		}
+	}
+	if (jinit >= 0)
+		cword=(jinit | (jinit << 8));
+	else if (jrev < 0)
+		cword=(rchr[hibyte(cword)] | (rchr[lobyte(cword)] << 8));
+	for (j=0;j<len;j++) {
+		cword=icrctb[(jrev < 0 ? rchr[(unsigned char) bufptr[j]] :
+			(unsigned char) bufptr[j]) ^ hibyte(cword)] ^ (lobyte(cword) << 8);
+	}
+	return (jrev >= 0 ? cword :
+		rchr[hibyte(cword)] | (rchr[lobyte(cword)] << 8));
+}