x86カルトクイズ(解ç”ç·¨) (mitsunari@cybozu labs)å•é¡Œç·¨ã¯ã“ã¡ã‚‰ã®x86カルトクイズã§ã™ï¼Ž Q1 [ä¹—ç®—ã®å‰Šæ¸›] lea eax, [eax + eax*8] lea eax, [eax + eax*4] 45 = 9 * 5 = (8 + 1) * (4 + 1)を利用ã™ã‚‹ï¼Žä¹—算命令ãŒé€Ÿããªã£ãŸã¨ã¯ã„ãˆï¼Œã¾ã add/sub/shift/leaã®çµ„ã¿åˆã‚ã›ã‚’使ã£ãŸæ–¹ãŒé€Ÿã„ã“ã¨ãŒå¤šã„． Q2 [æ¡ä»¶åˆ†å²ã®å‰Šæ¸›] cdq xor eax, edx sub eax, edx æ¡ä»¶åˆ†å²ã¯å¯èƒ½ãªé™ã‚Šä½¿ã‚ãªã„．次ã®äºŒã¤ã®æ’ç‰å¼ -x = x ^ (-1) - (-1) x = x ^ 0 - 0 㨠unsigned int m = (x < 0) ? -1 : 0 を組ã¿åˆã‚ã›ã‚‹ã“ã¨ã§çµ¶å¯¾å€¤ã‚’ unsigned int m = x >> 31; return x ^ m - m; ã¨å®Ÿç¾ã™ã‚‹ï¼Žã“ã“ã§mã‚’å–å¾—ã™ã‚‹éƒ¨åˆ†ã¯ mov edx, eax sa
x86カルトクイズ (mitsunari@cybozu labs)
Xbyakã§å§‹ã‚ã‚‹x86(IA-32)入門(2-1) (mitsunari@cybozu labs)
Xbyakã§å§‹ã‚ã‚‹x86(IA-32)入門 (mitsunari@cybozu labs)
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