f6e358483b
This patch adds a bit of optimized assembly code to the ipchksum() algorithm for x86 targets in order to take advantage of larger load sizes and the add-with-carry instruction. The same assembly (with one minor manual tweak) works for both 32 and 64 bit mode (with most of the work being done by GCC which automatically inserts `rax` or `eax` in the inline assembly depending on the build target). Change-Id: I484620dc14679ff5ca02b2ced2f84650730a6efc Signed-off-by: Julius Werner <jwerner@chromium.org> Reviewed-on: https://review.coreboot.org/c/coreboot/+/80255 Reviewed-by: Arthur Heymans <arthur@aheymans.xyz> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
101 lines
2.7 KiB
C
101 lines
2.7 KiB
C
/* SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0-or-later */
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#include <commonlib/bsd/ipchksum.h>
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/* See RFC 1071 for mathematical explanations of why we can first sum in a larger register and
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then narrow down, why we don't need to worry about endianness, etc. */
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uint16_t ipchksum(const void *data, size_t size)
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{
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const uint8_t *p1 = data;
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unsigned long wide_sum = 0;
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uint32_t sum = 0;
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size_t i = 0;
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#if defined(__aarch64__)
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size_t size16 = size / 16;
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const uint64_t *p8 = data;
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if (size16) {
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unsigned long tmp1, tmp2;
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i = size16 * 16;
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asm (
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"adds xzr, xzr, xzr\n\t" /* init carry flag for addition */
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"1:\n\t"
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"ldp %[v1], %[v2], [%[p8]], #16\n\t"
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"adcs %[wsum], %[wsum], %[v1]\n\t"
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"adcs %[wsum], %[wsum], %[v2]\n\t"
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"sub %[size16], %[size16], #1\n\t"
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"cbnz %[size16], 1b\n\t"
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"adcs %[wsum], %[wsum], xzr\n\t" /* use up last carry */
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: [v1] "=r" (tmp1),
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[v2] "=r" (tmp2),
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[wsum] "+r" (wide_sum),
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[p8] "+r" (p8),
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[size16] "+r" (size16)
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:: "cc"
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);
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}
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#elif defined(__i386__) || defined(__x86_64__)
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size_t size8 = size / 8;
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const uint64_t *p8 = data;
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i = size8 * 8;
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asm (
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"clc\n\t"
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"1:\n\t"
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"jecxz 2f\n\t" /* technically RCX on 64, but not gonna be that big */
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"adc (%[p8]), %[wsum]\n\t"
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#if defined(__i386__)
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"adc 4(%[p8]), %[wsum]\n\t"
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#endif /* __i386__ */
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"lea -1(%[size8]), %[size8]\n\t" /* Use LEA as a makeshift ADD that */
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"lea 8(%[p8]), %[p8]\n\t" /* doesn't modify the carry flag. */
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"jmp 1b\n\t"
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"2:\n\t"
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"setc %b[size8]\n\t" /* reuse size register to save last carry */
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"add %[size8], %[wsum]\n\t"
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: [wsum] "+r" (wide_sum),
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[p8] "+r" (p8),
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[size8] "+c" (size8) /* put size in ECX so we can JECXZ */
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:: "cc"
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);
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#endif /* __i386__ || __x86_64__ */
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while (wide_sum) {
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sum += wide_sum & 0xFFFF;
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wide_sum >>= 16;
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}
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sum = (sum & 0xFFFF) + (sum >> 16);
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for (; i < size; i++) {
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uint32_t v = p1[i];
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if (i % 2)
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v <<= 8;
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sum += v;
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/* Doing this unconditionally seems to be faster. */
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sum = (sum & 0xFFFF) + (sum >> 16);
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}
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return (uint16_t)~sum;
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}
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uint16_t ipchksum_add(size_t offset, uint16_t first, uint16_t second)
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{
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first = ~first;
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second = ~second;
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/*
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* Since the checksum is calculated in 16-bit chunks, if the offset at which
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* the data covered by the second checksum would start (if both data streams
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* came one after the other) is odd, that means the second stream starts in
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* the middle of a 16-bit chunk. This means the second checksum is byte
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* swapped compared to what we need it to be, and we must swap it back.
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*/
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if (offset % 2)
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second = (second >> 8) | (second << 8);
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uint32_t sum = first + second;
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sum = (sum & 0xFFFF) + (sum >> 16);
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return (uint16_t)~sum;
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}
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