varintBench.c

#include <stdlib.h>
#include <stdio.h>

typedef unsigned int u32;
typedef unsigned long long u64;

#define N 1000000
static u64 dataset[N];

static inline u64 rdtsc() {
#if defined(__x86_64__)
    u32 lo, hi;
    asm volatile("rdtsc" : "=a" (lo), "=d" (hi));
    return ((u64)hi << 32) | lo;
#elif defined(__aarch64__)
    u64 value;
    asm volatile("mrs %0, cntvct_el0" : "=r"(value));
    return value;
#endif
}

static size_t francesco(u64 value) {
    if (value <= 0x7F) return 1;
    if (value <= 0x3FFF) return 2;
    if (value <= 0x1FFFFF) return 3;
    if (value <= 0xFFFFFFF) return 4;
    if (value <= 0x7FFFFFFFF) return 5;
    if (value <= 0x3FFFFFFFFFF) return 6;
    if (value <= 0x1FFFFFFFFFFFF) return 7;
    if (value <= 0xFFFFFFFFFFFFFF) return 8;
    if (value <= 0x7FFFFFFFFFFFFFFF) return 9;
    return 10;
}

static size_t andrei(u64 value) {
    return (640 - __builtin_clzll(value | 1) * 9) / 64;
}

static size_t bara(u64 value) {
  size_t size = 1;
  while ((value = value >> 7)) {
    size++;
  }
  return size;
}

int main() {
  for (int i = 0; i < N; i++) {
    dataset[i] = (u64)(rand() & 0xff) << (rand() & 63);
  }

  u64 sink = 0;
  u64 before = rdtsc();
  for (int i = 0; i < N; ++i) sink += francesco(dataset[i]);
  u64 after = rdtsc();
  printf("Francesco: %08llu\n", after - before);

  before = rdtsc();
  for (int i = 0; i < N; ++i) sink += andrei(dataset[i]);
  after = rdtsc();
  printf("Andrei   : %08llu\n", after - before);

  before = rdtsc();
  for (int i = 0; i < N; ++i) sink += bara(dataset[i]);
  after = rdtsc();
  printf("Bara     : %08llu\n", after - before);

  printf("Sink ignore me: %llu\n", sink);
}