| smalluint i = index_in_str_array(params, name) + 1; |
| if (i == 0) |
| return 0; |
| if (!(i == 4 || i == 5)) |
| i |= 0x80; |
| |
| return i; |
| |
| I think that this optimization is wrong. |
| index_in_str_array returns int. At best, compiler will use it as-is. |
| At worst, compiler will try to make sure that it is properly cast |
| into a byte, which probably results in "n = n & 0xff" on many architectures. |
| |
| You save nothing on space here because i is not stored on-stack, |
| gcc will keep it in register. And even if it *is* stored, |
| it is *stack* storage, which is cheap (unlike data/bss). |
| |
| small[u]ints are useful _mostly_ for: |
| |
| (a) flag variables |
| (a1) global flag variables - make data/bss smaller |
| (a2) local flag variables - "a = 5", "a |= 0x40" are smaller |
| for bytes than for full integers. |
| Example: |
| on i386, there is no widening constant store instruction |
| for some types of address modes, thus |
| movl $0x0,(%eax) is "c7 00 00 00 00 00" |
| movb $0x0,(%eax) is "c6 00 00" |
| (b) small integer structure members, when you have many such |
| structures allocated, |
| or when these are global objects of this structure type |
| |
| small[u]ints are *NOT* useful for: |
| |
| (a) function parameters and return values - |
| they are pushed on-stack or stored in registers, bytes here are *harder* |
| to deal with than ints |
| (b) "computational" variables - "a++", "a = b*3 + 7" may take more code to do |
| on bytes than on ints on some architectires. |
