代码

// MSD radix: top-16 aligned-flush scatter + per-bucket 2-pass 8-bit LSD (port to n=1e8)
#include <string.h>
typedef unsigned int u32;
typedef unsigned char u8;
static u32 tmp[100000000 + (1<<20)];
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];
static u32 scratch[8192];
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; }
    const int B = 1 << 20;
    for (int b0 = 0; b0 < n; b0 += B) {
        int len = (b0 + B < n) ? B : (n - b0);
        for (i = 0; i < len; i++) {
            __builtin_prefetch(&src[b0+i+256],0,0);
            u32 x = src[b0 + i];
            u32 b = x >> 16;
            u32 p = pos[b];
            staging[b * 16 + p] = x;
            p++;
            if (p == 16) { u32 go = off[b]; 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) { u32 go = off[j]; memcpy(&dst[go], &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