blob: b57dfd7753fed34aabf3536aa48ec3de629caa10
1 | smalluint i = index_in_str_array(params, name) + 1; |
2 | if (i == 0) |
3 | return 0; |
4 | if (!(i == 4 || i == 5)) |
5 | i |= 0x80; |
6 | |
7 | return i; |
8 | |
9 | I think that this optimization is wrong. |
10 | index_in_str_array returns int. At best, compiler will use it as-is. |
11 | At worst, compiler will try to make sure that it is properly cast |
12 | into a byte, which probably results in "n = n & 0xff" on many architectures. |
13 | |
14 | You save nothing on space here because i is not stored on-stack, |
15 | gcc will keep it in register. And even if it *is* stored, |
16 | it is *stack* storage, which is cheap (unlike data/bss). |
17 | |
18 | small[u]ints are useful _mostly_ for: |
19 | |
20 | (a) flag variables |
21 | (a1) global flag variables - make data/bss smaller |
22 | (a2) local flag variables - "a = 5", "a |= 0x40" are smaller |
23 | for bytes than for full integers. |
24 | Example: |
25 | on i386, there is no widening constant store instruction |
26 | for some types of address modes, thus |
27 | movl $0x0,(%eax) is "c7 00 00 00 00 00" |
28 | movb $0x0,(%eax) is "c6 00 00" |
29 | (b) small integer structure members, when you have many such |
30 | structures allocated, |
31 | or when these are global objects of this structure type |
32 | |
33 | small[u]ints are *NOT* useful for: |
34 | |
35 | (a) function parameters and return values - |
36 | they are pushed on-stack or stored in registers, bytes here are *harder* |
37 | to deal with than ints |
38 | (b) "computational" variables - "a++", "a = b*3 + 7" may take more code to do |
39 | on bytes than on ints on some architectires. |
40 |