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