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wu :: forums    riddles    cs (Moderators: william wu, Icarus, SMQ, Grimbal, ThudnBlunder, Eigenray, towr)    REVERSE  bits in 8 byte « Previous topic | Next topic » Pages: 1  Reply Notify of replies Send Topic Print    Author  Topic: REVERSE  bits in 8 byte  (Read 6724 times) puzzlecracker Senior Riddler Men have become the tools of their tools     Gender: Posts: 319 REVERSE  bits in 8 byte   « on: Dec 17th, 2004, 11:33pm » Quote Modify Using C, but without loops or lookup tables, write a routine which reverses  the bits in an 8-bit byte       IP Logged While we are postponing, life speeds by John_Gaughan Uberpuzzler Behold, the power of cheese!     Gender: Posts: 767 Re: REVERSE  bits in 8 byte   « Reply #1 on: Dec 18th, 2004, 10:48am » Quote Modify This should do the trick. Can anyone make it shorter? :: unsigned char reverse (unsigned char n) {   return ((n & 0x01) << 7)   | ((n & 0x02) << 5)   | ((n & 0x04) << 3)   | ((n & 0x08) << 1)   | ((n & 0x10) >> 1)   | ((n & 0x20) >> 3)   | ((n & 0x40) >> 5)   | ((n & 0x80) >> 7); } :: IP Logged x = (0x2B | ~0x2B) x == the_question towr wu::riddles Moderator Uberpuzzler Some people are average, some are just mean.     Gender: Posts: 13730 Re: REVERSE  bits in 8 byte   « Reply #2 on: Dec 18th, 2004, 2:07pm » Quote Modify something like :: n = n&11110000 >>4 | n&00001111 << 4; n = n&11001100 >>2 | n&00110011 << 2; return  n&10101010 >>1 | n&01010101 << 1;   I didn't actually bothered to check whether this does what I think it ought to do, but if it doesn't it should give you the idea of what does.. :: IP Logged Wikipedia, Google, Mathworld, Integer sequence DB puzzlecracker Senior Riddler Men have become the tools of their tools     Gender: Posts: 319 Re: REVERSE  bits in 8 byte   « Reply #3 on: Dec 19th, 2004, 1:39pm » Quote Modify can both of you, or anyone else pretty much, explain that... thx        I thought to actually flipping the bits as    n=n^255, but only flips them....     I was wrong... please explain the logic.. thx   IP Logged While we are postponing, life speeds by puzzlecracker Senior Riddler Men have become the tools of their tools     Gender: Posts: 319 Re: REVERSE  bits in 8 byte   « Reply #4 on: Dec 19th, 2004, 3:23pm » Quote Modify never mind (i am an idiot) -- towr - you're a genous of modern creation! IP Logged While we are postponing, life speeds by Pages: 1  Reply Notify of replies Send Topic Print Forum Jump: ----------------------------- riddles -----------------------------  - easy   - medium   - hard   - what am i   - what happened   - microsoft => cs   - putnam exam (pure math)   - suggestions, help, and FAQ   - general problem-solving / chatting / whatever ----------------------------- general -----------------------------  - guestbook   - truth   - complex analysis   - wanted   - psychology   - chinese « Previous topic | Next topic »

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