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150 lines
3.5 KiB
C
150 lines
3.5 KiB
C
/*
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* arch/x86_64/lib/csum-partial.c
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*
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* This file contains network checksum routines that are better done
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* in an architecture-specific manner due to speed.
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*/
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#include <linux/compiler.h>
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#include <linux/export.h>
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#include <asm/checksum.h>
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static inline unsigned short from32to16(unsigned a)
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{
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unsigned short b = a >> 16;
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asm("addw %w2,%w0\n\t"
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"adcw $0,%w0\n"
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: "=r" (b)
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: "0" (b), "r" (a));
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return b;
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}
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/*
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* Do a 64-bit checksum on an arbitrary memory area.
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* Returns a 32bit checksum.
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*
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* This isn't as time critical as it used to be because many NICs
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* do hardware checksumming these days.
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*
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* Things tried and found to not make it faster:
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* Manual Prefetching
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* Unrolling to an 128 bytes inner loop.
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* Using interleaving with more registers to break the carry chains.
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*/
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static unsigned do_csum(const unsigned char *buff, unsigned len)
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{
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unsigned odd, count;
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unsigned long result = 0;
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if (unlikely(len == 0))
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return result;
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odd = 1 & (unsigned long) buff;
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if (unlikely(odd)) {
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result = *buff << 8;
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len--;
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buff++;
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}
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count = len >> 1; /* nr of 16-bit words.. */
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if (count) {
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if (2 & (unsigned long) buff) {
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result += *(unsigned short *)buff;
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count--;
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len -= 2;
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buff += 2;
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}
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count >>= 1; /* nr of 32-bit words.. */
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if (count) {
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unsigned long zero;
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unsigned count64;
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if (4 & (unsigned long) buff) {
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result += *(unsigned int *) buff;
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count--;
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len -= 4;
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buff += 4;
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}
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count >>= 1; /* nr of 64-bit words.. */
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/* main loop using 64byte blocks */
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zero = 0;
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count64 = count >> 3;
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while (count64) {
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asm("addq 0*8(%[src]),%[res]\n\t"
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"adcq 1*8(%[src]),%[res]\n\t"
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"adcq 2*8(%[src]),%[res]\n\t"
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"adcq 3*8(%[src]),%[res]\n\t"
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"adcq 4*8(%[src]),%[res]\n\t"
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"adcq 5*8(%[src]),%[res]\n\t"
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"adcq 6*8(%[src]),%[res]\n\t"
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"adcq 7*8(%[src]),%[res]\n\t"
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"adcq %[zero],%[res]"
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: [res] "=r" (result)
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: [src] "r" (buff), [zero] "r" (zero),
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"[res]" (result));
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buff += 64;
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count64--;
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}
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/* last up to 7 8byte blocks */
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count %= 8;
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while (count) {
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asm("addq %1,%0\n\t"
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"adcq %2,%0\n"
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: "=r" (result)
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: "m" (*(unsigned long *)buff),
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"r" (zero), "0" (result));
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--count;
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buff += 8;
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}
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result = add32_with_carry(result>>32,
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result&0xffffffff);
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if (len & 4) {
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result += *(unsigned int *) buff;
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buff += 4;
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}
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}
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if (len & 2) {
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result += *(unsigned short *) buff;
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buff += 2;
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}
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}
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if (len & 1)
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result += *buff;
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result = add32_with_carry(result>>32, result & 0xffffffff);
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if (unlikely(odd)) {
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result = from32to16(result);
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result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
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}
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return result;
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}
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/*
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* computes the checksum of a memory block at buff, length len,
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* and adds in "sum" (32-bit)
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*
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* returns a 32-bit number suitable for feeding into itself
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* or csum_tcpudp_magic
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*
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* this function must be called with even lengths, except
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* for the last fragment, which may be odd
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*
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* it's best to have buff aligned on a 64-bit boundary
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*/
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__wsum csum_partial(const void *buff, int len, __wsum sum)
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{
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return (__force __wsum)add32_with_carry(do_csum(buff, len),
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(__force u32)sum);
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}
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EXPORT_SYMBOL(csum_partial);
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/*
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* this routine is used for miscellaneous IP-like checksums, mainly
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* in icmp.c
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*/
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__sum16 ip_compute_csum(const void *buff, int len)
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{
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return csum_fold(csum_partial(buff,len,0));
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}
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EXPORT_SYMBOL(ip_compute_csum);
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