用于测试Collatz猜想的C ++代码比手写汇编要快-为什么？

问题：

I wrote these two solutions for Project Euler Q14 , in assembly and in C++. 我用汇编语言和C ++语言为Euler Q14项目编写了这两种解决方案。 They are the same identical brute force approach for testing the Collatz conjecture . 它们是用于测试Collatz猜想的相同相同的蛮力方法。 The assembly solution was assembled with 组装解决方案与

nasm -felf64 p14.asm && gcc p14.o -o p14

The C++ was compiled with C ++使用

g++ p14.cpp -o p14

Assembly, p14.asm 汇编， p14.asm

section .data
    fmt db "%d", 10, 0

global main
extern printf

section .text

main:
    mov rcx, 1000000
    xor rdi, rdi        ; max i
    xor rsi, rsi        ; i

l1:
    dec rcx
    xor r10, r10        ; count
    mov rax, rcx

l2:
    test rax, 1
    jpe even

    mov rbx, 3
    mul rbx
    inc rax
    jmp c1

even:
    mov rbx, 2
    xor rdx, rdx
    div rbx

c1:
    inc r10
    cmp rax, 1
    jne l2

    cmp rdi, r10
    cmovl rdi, r10
    cmovl rsi, rcx

    cmp rcx, 2
    jne l1

    mov rdi, fmt
    xor rax, rax
    call printf
    ret

C++, p14.cpp C ++，p14.cpp

#include <iostream>

using namespace std;

int sequence(long n) {
    int count = 1;
    while (n != 1) {
        if (n % 2 == 0)
            n /= 2;
        else
            n = n*3 + 1;

        ++count;
    }

    return count;
}

int main() {
    int max = 0, maxi;
    for (int i = 999999; i > 0; --i) {
        int s = sequence(i);
        if (s > max) {
            max = s;
            maxi = i;
        }
    }

    cout << maxi << endl;
}

I know about the compiler optimizations to improve speed and everything, but I don't see many ways to optimize my assembly solution further (speaking programmatically not mathematically). 我知道可以提高速度和所有方面的编译器优化，但是我看不到有很多方法可以进一步优化我的汇编解决方案（以编程方式而不是数学方式）。

The C++ code has modulus every term and division every even term, where assembly is only one division per even term. C ++代码的每项均具有模数，而每偶数项均具有模数，其中汇编仅是每偶数项除一。

But the assembly is taking on average 1 second longer than the C++ solution. 但是汇编程序比C ++解决方案平均要花费1秒钟的时间。 Why is this? 为什么是这样？ I am asking out of mainly curiosity. 我主要是出于好奇。

Execution times 执行时间

My system: 64 bit Linux on ‎1.4 GHz Intel Celeron 2955U (Haswell microarchitecture). 我的系统：1.4 GHz Intel Celeron 2955U（Haswell微体系结构）上的64位Linux。

g++ (unoptimized): avg 1272 ms g++ （未优化）：平均1272毫秒
g++ -O3 avg 578 ms g++ -O3平均578毫秒
original asm (div) avg 2650 ms 原始ASM（div）平均2650毫秒
Asm (shr) avg 679 ms Asm (shr)平均679毫秒
@johnfound asm , assembled with nasm avg 501 ms @johnfound asm ，与nasm平均501毫秒组合
@hidefromkgb asm avg 200 ms @hidefromkgb asm平均200毫秒
@hidefromkgb asm optimized by @Peter Cordes avg 145 ms @hidefromkgb asm由@Peter Cordes优化 145毫秒
@Veedrac C++ avg 81 ms with -O3 , 305 ms with -O0 @Veedrac C ++使用-O3平均81 ms，使用-O0平均305 ms