[英]Assembly negation in msp430
I have the following versions of negating some integer value (in R12) in assembly in msp430:在 msp430 的汇编中,我有以下版本的否定一些 integer 值(在 R12 中):
inv R12
inc R12
this is according to the manual and I think this will work the same?这是根据手册,我认为这会起作用吗?
inv R12
add #1, R12
But will this work and why not?但这会奏效吗?为什么不呢? : :
sub #1, R12
inv R12
Still new to this and thank you for any help!对此仍然很陌生,感谢您的帮助!
INC dst
is emulated with ADD #1, dst
, so the first two versions are exactly the same. INC dst
使用ADD #1, dst
进行模拟,因此前两个版本完全相同。
As for the third version: In the two's complement representation, inverting all bits computes the negative minus one, so you are computing (− x − 1) + 1 or −( x + 1) + 1, which is indeed the same.至于第三个版本:在二进制补码表示中,将所有位取反计算负一,因此您正在计算 (- x - 1) + 1 或 -( x + 1) + 1,这确实是相同的。
And if you want a more practical demonstration, just use brute force:如果您想要更实际的演示,只需使用蛮力:
#include <assert.h>
#include <stdint.h>
#include <stdio.h>
int main()
{
for (uint32_t i = 0; i < 0x10000; i++) {
uint16_t input = i;
uint16_t output1 = (~input) + 1;
uint16_t output2 = ~(input - 1);
assert(output1 == output2);
}
puts("it works!");
return 0;
}
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