代码

#include <string.h>
#include <stdint.h>
typedef unsigned int u32;
typedef unsigned char u8;

static u32 tmp[(1u<<27) + (1u<<21)] __attribute__((aligned(64)));
static u32 cnt[65536];
static u32 rbase[65536];
static u32 pbase[65536];
static u32 off[65536];
static u8 pos[65536];
static u32 staging[65536 * 16] __attribute__((aligned(64)));
static u32 scratch[8192] __attribute__((aligned(64)));
static u32 bc[256];

static void radix16_top(u32 *src, u32 *dst, int n) {
    int i, j;
    for (j = 0; j < 65536; j++) cnt[j] = 0;
    for (i = 0; i < n; i++) { __builtin_prefetch(&src[i+256],0,0); cnt[src[i] >> 16]++; }
    { u32 t = 0, p = 0; for (j = 0; j < 65536; j++) { u32 c = cnt[j]; rbase[j] = t; pbase[j] = p; t += c; p = (p + c + 15) & ~15u; } }
    for (j = 0; j < 65536; j++) { off[j] = pbase[j]; pos[j] = 0; }

    #define K 16
    u32 bk[K];
    for (int k = 0; k < K && k < n; k++) {
        u32 b = src[k] >> 16;
        bk[k] = b;
        __builtin_prefetch(&pos[b]);
        __builtin_prefetch(&staging[b*16]);
    }
    int iend = n - K;
    for (i = 0; i < iend; i++) {
        u32 b = bk[i & (K-1)];
        u32 x = src[i];
        u32 p = pos[b];
        staging[b*16+p] = x;
        p++;
        if (p == 16) { u32 go = off[b]; __builtin_memcpy(dst+go, staging+b*16, 64); off[b] = go + 16; p = 0; }
        pos[b] = (u8)p;
        // prefetch for element i+K
        u32 f = i + K;
        u32 bf = src[f] >> 16;
        bk[i & (K-1)] = bf;
        __builtin_prefetch(&pos[bf]);
        __builtin_prefetch(&staging[bf*16]);
    }
    for (; i < n; i++) {
        u32 b = bk[i & (K-1)];
        u32 x = src[i];
        u32 p = pos[b];
        staging[b*16+p] = x;
        p++;
        if (p == 16) { u32 go = off[b]; __builtin_memcpy(dst+go, staging+b*16, 64); off[b] = go + 16; p = 0; }
        pos[b] = (u8)p;
    }
    for (j = 0; j < 65536; j++) { u32 p = pos[j]; if (p > 0) memcpy(dst+off[j], staging+j*16, p*4); }
}

static void sort_bucket(u32 *src, u32 *dst, int m) {
    int i, j;
    for (j = 0; j < 256; j++) bc[j] = 0;
    for (i = 0; i < m; i++) bc[src[i] & 255]++;
    for (j = 1; j < 256; j++) bc[j] += bc[j-1];
    for (i = m - 1; i >= 0; i--) { u32 x = src[i]; scratch[--bc[x & 255]] = x; }
    for (j = 0; j < 256; j++) bc[j] = 0;
    for (i = 0; i < m; i++) bc[(scratch[i] >> 8) & 255]++;
    for (j = 1; j < 256; j++) bc[j] += bc[j-1];
    for (i = m - 1; i >= 0; i--) { u32 x = scratch[i]; dst[--bc[(x >> 8) & 255]] = x; }
}

void sort(unsigned *aa, int n) {
    u32 *a = (u32*)aa;
    int j;
    radix16_top(a, tmp, n);
    for (j = 0; j < 65536; j++) {
        int m = (int)cnt[j];
        if (m > 0) sort_bucket(tmp + pbase[j], a + rbase[j], m);
    }
}

评测结果