ref: a288db973cf0436575a3e660d2a1c68adbee9e56
dir: /sys/src/libip/ptclbsum.c/
#include <u.h> #include <libc.h> #include <ip.h> static short endian = 1; static uchar* aendian = (uchar*)&endian; #define LITTLE *aendian ushort ptclbsum(uchar *addr, int len) { ulong losum, hisum, mdsum, x; ulong t1, t2; losum = 0; hisum = 0; mdsum = 0; x = 0; if((uintptr)addr & 1) { if(len) { hisum += addr[0]; len--; addr++; } x = 1; } while(len >= 16) { t1 = *(ushort*)(addr+0); t2 = *(ushort*)(addr+2); mdsum += t1; t1 = *(ushort*)(addr+4); mdsum += t2; t2 = *(ushort*)(addr+6); mdsum += t1; t1 = *(ushort*)(addr+8); mdsum += t2; t2 = *(ushort*)(addr+10); mdsum += t1; t1 = *(ushort*)(addr+12); mdsum += t2; t2 = *(ushort*)(addr+14); mdsum += t1; mdsum += t2; len -= 16; addr += 16; } while(len >= 2) { mdsum += *(ushort*)addr; len -= 2; addr += 2; } if(x) { if(len) losum += addr[0]; if(LITTLE) losum += mdsum; else hisum += mdsum; } else { if(len) hisum += addr[0]; if(LITTLE) hisum += mdsum; else losum += mdsum; } losum += hisum >> 8; losum += (hisum & 0xff) << 8; while(hisum = losum>>16) losum = hisum + (losum & 0xffff); return losum & 0xffff; }