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English fixes to docs/smallint.txt

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2010-10-24 03:23:59 +02:00
parent 8f8ee534a7
commit 738e4de013
1 changed files with 5 additions and 3 deletions
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8
docs/smallint.txt
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@ -8,14 +8,15 @@
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 casted
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 it is *is* stored,
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
@ -26,10 +27,11 @@ small[u]ints are useful _mostly_ for:
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,
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