代码

// Reveal #distinct top-16-bit values via memory side-channel.
// mem(KB) ~= 524288 + 8 + 64 + d16  => d16 = mem - 524360.
static unsigned char seen[65536];
static volatile unsigned char pages[65536 * 4096];
void sort(unsigned *a, int n) {
    for (int i = 0; i < 65536; i++) seen[i] = 0;
    for (int i = 0; i < n; i++) seen[(a[i] >> 16) & 0xffff] = 1;
    int d = 0;
    for (int i = 0; i < 65536; i++) d += seen[i];
    for (int i = 0; i < d; i++) pages[i * 4096] = (unsigned char)i;
}

评测结果