Upstream: smooth weighted round-robin balancing. For edge case weights like { 5, 1, 1 } we now produce { a, a, b, a, c, a, a } sequence instead of { c, b, a, a, a, a, a } produced previously. Algorithm is as follows: on each peer selection we increase current_weight of each eligible peer by its weight, select peer with greatest current_weight and reduce its current_weight by total number of weight points distributed among peers. In case of { 5, 1, 1 } weights this gives the following sequence of current_weight's: a b c 0 0 0 (initial state) 5 1 1 (a selected) -2 1 1 3 2 2 (a selected) -4 2 2 1 3 3 (b selected) 1 -4 3 6 -3 4 (a selected) -1 -3 4 4 -2 5 (c selected) 4 -2 -2 9 -1 -1 (a selected) 2 -1 -1 7 0 0 (a selected) 0 0 0 To preserve weight reduction in case of failures the effective_weight variable was introduced, which usually matches peer's weight, but is reduced temporarily on peer failures. This change also fixes loop with backup servers and proxy_next_upstream http_404 (ticket #47), and skipping alive upstreams in some cases if there are multiple dead ones (ticket #64).

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#ifndef _NGX_CRC_H_INCLUDED_
#define _NGX_CRC_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


/* 32-bit crc16 */

static ngx_inline uint32_t
ngx_crc(u_char *data, size_t len)
{
    uint32_t  sum;

    for (sum = 0; len; len--) {

        /*
         * gcc 2.95.2 x86 and icc 7.1.006 compile
         * that operator into the single "rol" opcode,
         * msvc 6.0sp2 compiles it into four opcodes.
         */
        sum = sum >> 1 | sum << 31;

        sum += *data++;
    }

    return sum;
}


#endif /* _NGX_CRC_H_INCLUDED_ */