| I don't think the 8-bit CPU instruction sets were designed with code-generation for high-level languages in mind, but to make it easier to write assembly by hand. And each 8-bit CPU had its specialties, and it wasn't uncommon that computers were designed around those specialties. For instance when you look at the video memory layout of Z80 computers like the ZX Spectrum or CPC, those often have a weird non-linear arrangement, which only makes sense with the special 16-bit register pairs on the Z80. E.g. when the 16-bit register pair HL is used as a video memory address, the memory layout was often such that H and L could basically be used as X and Y coordinates. E.g. incrementing L gets you to the next character on the same line, and incrementing H to the first pixel line of the character line below. The KC85/4 (East German home computer) even had a 90 degree rotated memory layout of 320x256 pixels, 8 horizontal pixels grouped in a byte, so the video memory was a matrix of 40 columns by 256 lines. Put the column (0..39) into H, and the line (0..255) into L, and you have the complete video memory address (or rather offset, H must 0x80 + column, because video memory started at 0x8000). Increment or decrement H to move to the next or previous column, and L to get to the next or previous line. edit: messed up the number of columns, it's 40, not 80 :) |
The instruction set was very limited (in comparison to i386 etc.) so the learning curve was not steep and writing in assembler was, in practice, no more time consuming than using C now - once you were in the flow.
However due to the resource constraints you not only had to dry out everything into functions as you would with C today - but often had to manually mutate parts of the function instruction set code by poking in new values before calling to change the behaviour to avoid wasting memory on branches etc.
For large writes people would often move the stack pointer around as PUSH BC etc. were faster than LD at writing an address and inc(dec?) the pointer. I seem to remember IX/IY being avoided as much as poss as they were quite costly.