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I want to convert a positive number to negative in assembly, I need a code sample
The input is in hex sdword
Thanks
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Negative numbers are represented in Two's Complement in assembly. In order to obtain Two's Complement of a number you have two options: to complement all it's bits and add one. to complement all it's bits until the last 1.
With only one exception, starting with any number in two's-complement representation, if all the bits are flipped and 1 added, the two's-complement representation of the negative of that number is obtained. Positive 12 becomes negative 12, positive 5 becomes negative 5, zero becomes zero(+overflow), etc.
To convert positive int to negative and vice-versa, use the Bitwise Complement Operator.
You are processing floating point numbers by using integer instructions and want to invert the sign: In this case you have to change the sign bit. This is done using x xor 0x80000000 . On MIPS CPUs, you can generate the constant 0x80000000 using one lui instruction.
Well, there are two ways to do this, best would be to load the number into a register, then use the NEG instruction as Hans mention, ie: NEG EAX would negate eax. The other way would be XOR EAX,EAX SUB EAX,EDX where edx contains the number you want to negate
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