| ▲ | miningape 3 hours ago |
| Loving this series! I'm currently implementing a z80 emulator (gameboy) and it's my first real introduction to CISC, and is really pushing my assembly / machine code skills - so having these blog posts coming from the "other direction" are really interesting and give me some good context. I've implemented toy languages and bytecode compilers/vms before but seeing it from a professional perspective is just fascinating. That being said it was totally unexpected to find out we can use "addresses" for addition on x86. |
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| ▲ | Joker_vD 3 hours ago | parent [-] |
| A seasoned C programmer knows that "&arr[index]" is really just "arr + index" :) So in a sense, the optimizer rewrote "x + y" into "(int)&(((char*)x)[y])", which looks scarier in C, I admit. |
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| ▲ | crote 2 hours ago | parent [-] | | The horrifying side effect of this is that "arr[idx]" is equal to "idx[arr]", so "5[arr]" is just as valid as "arr[5]". Your colleagues would probably prefer if you forget this. | | |
| ▲ | miningape 2 hours ago | parent | next [-] | | Mom, please come pick me up. These kids are scaring me. | |
| ▲ | Joker_vD 2 hours ago | parent | prev | next [-] | | > so "5[arr]" is just as valid as "arr[5]" This is, I am sure, one of the stupid legacy reasons we still write "lr a0, 4(a1)" instead of more sensible "lr a0, a1[4]". The other one is that FORTRAN used round parentheses for both array access and function calls, so it stuck somehow. | |
| ▲ | rocqua 2 hours ago | parent | prev [-] | | That depends on sizeof(*arr) no? | | |
| ▲ | unwind 2 hours ago | parent | next [-] | | Not in C no, since arithmetic on a pointer is implicitly scaled by the size of the value being pointed at (this statement is kind of breaking the abstraction ... oh well). | |
| ▲ | messe an hour ago | parent | prev [-] | | Nope, a[b] is equivalent to *(a + b) regardless of a and b. | | |
| ▲ | sureglymop an hour ago | parent [-] | | Given that, why don't we use just `*(a + b)` everywhere? Wouldn't that be more verbose and less confusing? (genuinely asking) | | |
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