# Difference between revisions of "Talk:Script"

(Created page with "OP_IFDUP 115 0x73 x x / x x If the input is true or false, duplicate it. Shouldn't it be: "If the input is true, duplicate it."? --~~~~") |
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− | + | xOP_IFDUP 115 0x73 x x / x x If the input is true or false, duplicate it. | |

Shouldn't it be: "If the input is true, duplicate it."? | Shouldn't it be: "If the input is true, duplicate it."? | ||

--[[User:ThePiachu|ThePiachu]] 11:37, 20 December 2011 (GMT) | --[[User:ThePiachu|ThePiachu]] 11:37, 20 December 2011 (GMT) | ||

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+ | The byte vectors in the stack are specified as being signed integers or variable-length. Then there's an explanation that these integers are considered false if they are either zero or negative zero, which is 0x80. This is an old binary representation called sign-magnitude, which is important to state, since today virtually all computers use two's complement as representation, and there's no such thing as a negative zero there. There's even another representation, one's complement, where negative zero looks like 0xff. | ||

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+ | Reading the source code of the application, I see that arithmetic operations expect unsigned integers, for example, operations OP_2MUL and OP_2DIV are implemented as byte-shifting, which wouldn't work with signed representations. | ||

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+ | --[[User:Jpierre|Jpierre]] 10:43, 4 March 2012 (GMT) |

## Revision as of 10:43, 4 March 2012

xOP_IFDUP 115 0x73 x x / x x If the input is true or false, duplicate it.

Shouldn't it be: "If the input is true, duplicate it."? --ThePiachu 11:37, 20 December 2011 (GMT)

The byte vectors in the stack are specified as being signed integers or variable-length. Then there's an explanation that these integers are considered false if they are either zero or negative zero, which is 0x80. This is an old binary representation called sign-magnitude, which is important to state, since today virtually all computers use two's complement as representation, and there's no such thing as a negative zero there. There's even another representation, one's complement, where negative zero looks like 0xff.

Reading the source code of the application, I see that arithmetic operations expect unsigned integers, for example, operations OP_2MUL and OP_2DIV are implemented as byte-shifting, which wouldn't work with signed representations.

--Jpierre 10:43, 4 March 2012 (GMT)