Switch branches/tags
Nothing to show
Find file
Fetching contributors…
Cannot retrieve contributors at this time
40 lines (32 sloc) 1.5 KB
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.
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.