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Instruction for the day |
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adrianl (12:19 24/8/2006)
VincceH (07:31 25/8/2006)
Phlamethrower (09:48 25/8/2006)
VincceH (19:34 25/8/2006)
adrianl (11:38 25/8/2006)
Phlamethrower (11:42 25/8/2006)
adrianl (12:21 25/8/2006)
ninj (13:11 25/8/2006)
Phlamethrower (14:22 25/8/2006)
ninj (14:35 25/8/2006)
adrianl (14:42 25/8/2006)
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Adrian Lees |
Message #79141, posted by adrianl at 12:19, 24/8/2006 |
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Posts: 1637
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BIC R0,R0,R0,ASR #31 |
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VinceH |
Message #79179, posted by VincceH at 07:31, 25/8/2006, in reply to message #79141 |
 Lowering the tone since the dawn of time
Posts: 1600
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My ARM assembler was never very good, but with the aid of google to remind myself what BIC and ASR actually do... (before I look, I think BIC is a pen - I mean, bit clear, and ASR is probably arithmetic shift right)
(Yup)
So...
Shift the contents of R0 right by 31 bits - so either every bit is 1 or 0 depending if the MSB was 1 or 0 - then use the result to perform a bit clear on R0.
Result: If the MSB is set (ie the contents are a -ve number) R0 will finish up containing zero. If the MSB is clear (ie the contents are a +ve number) R0 will finish up contianing that number.
What's my prize? |
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Jeffrey Lee |
Message #79184, posted by Phlamethrower at 09:48, 25/8/2006, in reply to message #79179 |
 Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot stuff
Posts: 15100
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What's my prize? A single instruction to ensure a number is >= 0?  |
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Adrian Lees |
Message #79188, posted by adrianl at 11:38, 25/8/2006, in reply to message #79141 |
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TEQ R0,R0,ROR #1 |
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Jeffrey Lee |
Message #79189, posted by Phlamethrower at 11:42, 25/8/2006, in reply to message #79188 |
Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot stuff
Posts: 15100
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Check if a number is 0 or -1? |
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Adrian Lees |
Message #79191, posted by adrianl at 12:21, 25/8/2006, in reply to message #79189 |
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Uh huh |
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ninjah |
Message #79193, posted by ninj at 13:11, 25/8/2006, in reply to message #79189 |
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Posts: 288
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Check if a number is 0 or -1? EOR R0, R0, R0 ASR #31 ? |
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Jeffrey Lee |
Message #79194, posted by Phlamethrower at 14:22, 25/8/2006, in reply to message #79193 |
Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot stuff
Posts: 15100
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Check if a number is 0 or -1? EOR R0, R0, R0 ASR #31 ?
No, that sets a number to zero if it's -1  |
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ninjah |
Message #79195, posted by ninj at 14:35, 25/8/2006, in reply to message #79194 |
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Posts: 288
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Check if a number is 0 or -1? EOR R0, R0, R0 ASR #31 ?
No, that sets a number to zero if it's -1
Or if it's already 0. And not otherwise. |
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Adrian Lees |
Message #79196, posted by adrianl at 14:42, 25/8/2006, in reply to message #79195 |
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Posts: 1637
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if (a < 0) a = -(a + 1)
ie. it's actually ABS(a) if a is in one's complement. which nobody uses
[Edited by adrianl at 15:49, 25/8/2006] |
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VinceH |
Message #79203, posted by VincceH at 19:34, 25/8/2006, in reply to message #79184 |
Lowering the tone since the dawn of time
Posts: 1600
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What's my prize? A single instruction to ensure a number is >= 0?
As long as it comes with a free Iyonix, that's fine.  |
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