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.