PHP 是否优化尾递归?

编程入门行业动态更新时间:2024-10-10 09:15:35

本文介绍了PHP 是否优化尾递归?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！问题描述

我写了一小段代码，如果优化尾递归，我相信它应该会成功，但是它炸毁了堆栈.我应该得出结论 PHP 没有优化尾递归吗?

I wrote a small piece of code that I believe should have succeeded if tail recursion was optimized, however it blew up the stack. Should I conclude PHP does not optimize tail recursion?

function sumrand($n,$sum) { if ($n== 0) { return $sum; } else { return (sumrand($n-1,$sum+rand(0,1))); } } echo sumrand(500000,0)." ";

推荐答案

以下是为此生成的操作码(对于奇怪的表示表示抱歉):

Here are the generated opcodes for that (sorry for the strange representation):

Global ------------------------------------------------------------------------------- BCDCAC 0003: NOP () BCDD24 0012: SEND_VAL (CONST: "500000") BCDD9C 0012: SEND_VAL (CONST: NULL) BCDE14 0012: DO_FCALL (CONST: "sumrand") -> VAR 0 BCDE8C 0012: CONCAT (VAR 0, CONST: " ") -> TMP_VAR 1 BCDF04 0012: ECHO (TMP_VAR 1) BCDF7C 0014: RETURN (CONST: "1") Functions ------------------------------------------------------------------------------- sumrand (17 op) BCFABC 0003: RECV (CONST: "1") -> CV 0 ($n) BCFB34 0003: RECV (CONST: "2") -> CV 1 ($sum) BCFBAC 0004: IS_EQUAL (CV 0 ($n), CONST: NULL) -> TMP_VAR 0 BCFC24 0004: JMPZ (TMP_VAR 0, &(BCFD18+6)) BCFC9C 0005: RETURN (CV 1 ($sum)) BCFD14 0006: JMP (&(BD01C8+10)) BCFD8C 0008: INIT_FCALL_BY_NAME (NULL, CONST: "sumrand") BCFE04 0008: SUB (CV 0 ($n), CONST: "1") -> TMP_VAR 1 BCFE7C 0008: SEND_VAL (TMP_VAR 1) BCFEF4 0008: SEND_VAL (CONST: NULL) BCFF6C 0008: SEND_VAL (CONST: "1") BCFFE4 0008: DO_FCALL (CONST: "rand") -> VAR 2 BD005C 0008: ADD (CV 1 ($sum), VAR 2) -> TMP_VAR 3 BD00D4 0008: SEND_VAL (TMP_VAR 3) BD014C 0008: DO_FCALL_BY_NAME () -> VAR 4 BD01C4 0008: RETURN (VAR 4) BD023C 0010: RETURN (CONST: NULL)