URL
https://opencores.org/ocsvn/openrisc/openrisc/trunk
Subversion Repositories openrisc
[/] [openrisc/] [trunk/] [rtos/] [rtems/] [c/] [src/] [libnetworking/] [netinet/] [in_cksum_i386.c] - Rev 227
Go to most recent revision | Compare with Previous | Blame | View Log
/* * Checksum routine for Internet Protocol family headers. * * This routine is very heavily used in the network * code and should be modified for each CPU to be as fast as possible. * * This implementation is 386 version. * * $Id: in_cksum_i386.c,v 1.2 2001-09-27 12:01:55 chris Exp $ */ #include <stdio.h> /* for puts */ #undef ADDCARRY #define ADDCARRY(x) if ((x) > 0xffff) (x) -= 0xffff #define REDUCE {sum = (sum & 0xffff) + (sum >> 16); ADDCARRY(sum);} /* * Thanks to gcc we don't have to guess * which registers contain sum & w. */ #define ADD(n) asm("addl " #n "(%2), %0" : "=r" (sum) : "0" (sum), "r" (w)) #define ADDC(n) asm("adcl " #n "(%2), %0" : "=r" (sum) : "0" (sum), "r" (w)) #define LOAD(n) asm volatile("movb " #n "(%1), %0" : "=r" (junk) : "r" (w)) #define MOP asm("adcl $0, %0" : "=r" (sum) : "0" (sum)) int in_cksum(m, len) register struct mbuf *m; register int len; { register u_short *w; register unsigned sum = 0; register int mlen = 0; int byte_swapped = 0; union { char c[2]; u_short s; } su; for (;m && len; m = m->m_next) { if (m->m_len == 0) continue; w = mtod(m, u_short *); if (mlen == -1) { /* * The first byte of this mbuf is the continuation * of a word spanning between this mbuf and the * last mbuf. */ /* su.c[0] is already saved when scanning previous * mbuf. sum was REDUCEd when we found mlen == -1 */ su.c[1] = *(u_char *)w; sum += su.s; w = (u_short *)((char *)w + 1); mlen = m->m_len - 1; len--; } else mlen = m->m_len; if (len < mlen) mlen = len; len -= mlen; /* * Force to long boundary so we do longword aligned * memory operations */ if (3 & (int) w) { REDUCE; if ((1 & (int) w) && (mlen > 0)) { sum <<= 8; su.c[0] = *(char *)w; w = (u_short *)((char *)w + 1); mlen--; byte_swapped = 1; } if ((2 & (int) w) && (mlen >= 2)) { sum += *w++; mlen -= 2; } } /* * Advance to a 486 cache line boundary. */ if (4 & (int) w && mlen >= 4) { ADD(0); MOP; w += 2; mlen -= 4; } if (8 & (int) w && mlen >= 8) { ADD(0); ADDC(4); MOP; w += 4; mlen -= 8; } /* * Do as much of the checksum as possible 32 bits at at time. * In fact, this loop is unrolled to make overhead from * branches &c small. */ mlen -= 1; while ((mlen -= 32) >= 0) { u_char junk; /* * Add with carry 16 words and fold in the last * carry by adding a 0 with carry. * * The early ADD(16) and the LOAD(32) are to load * the next 2 cache lines in advance on 486's. The * 486 has a penalty of 2 clock cycles for loading * a cache line, plus whatever time the external * memory takes to load the first word(s) addressed. * These penalties are unavoidable. Subsequent * accesses to a cache line being loaded (and to * other external memory?) are delayed until the * whole load finishes. These penalties are mostly * avoided by not accessing external memory for * 8 cycles after the ADD(16) and 12 cycles after * the LOAD(32). The loop terminates when mlen * is initially 33 (not 32) to guaranteed that * the LOAD(32) is within bounds. */ ADD(16); ADDC(0); ADDC(4); ADDC(8); ADDC(12); LOAD(32); ADDC(20); ADDC(24); ADDC(28); MOP; w += 16; } mlen += 32 + 1; if (mlen >= 32) { ADD(16); ADDC(0); ADDC(4); ADDC(8); ADDC(12); ADDC(20); ADDC(24); ADDC(28); MOP; w += 16; mlen -= 32; } if (mlen >= 16) { ADD(0); ADDC(4); ADDC(8); ADDC(12); MOP; w += 8; mlen -= 16; } if (mlen >= 8) { ADD(0); ADDC(4); MOP; w += 4; mlen -= 8; } if (mlen == 0 && byte_swapped == 0) continue; /* worth 1% maybe ?? */ REDUCE; while ((mlen -= 2) >= 0) { sum += *w++; } if (byte_swapped) { sum <<= 8; byte_swapped = 0; if (mlen == -1) { su.c[1] = *(char *)w; sum += su.s; mlen = 0; } else mlen = -1; } else if (mlen == -1) /* * This mbuf has odd number of bytes. * There could be a word split betwen * this mbuf and the next mbuf. * Save the last byte (to prepend to next mbuf). */ su.c[0] = *(char *)w; } if (len) puts("cksum: out of data"); if (mlen == -1) { /* The last mbuf has odd # of bytes. Follow the standard (the odd byte is shifted left by 8 bits) */ su.c[1] = 0; sum += su.s; } REDUCE; return (~sum & 0xffff); }
Go to most recent revision | Compare with Previous | Blame | View Log