Author: Gerd Isenberg
Date: 01:14:35 01/17/04
Go up one level in this thread
On January 16, 2004 at 22:15:34, Federico Corigliano wrote:
>Hi
>
>In my engine I have a lot of #defines as:
>#define FileA 0xFFFFFFFF <- I don't remember the real value
>and I want to convert it to:
>const UINT64 FileA = 0xFFFFFFFFF;
>I the change can affect the speed. As I often use MSVC Debugger, it's boring to
>translate every #define to the respective number.
>
>Federico
For assembler instructions that means immediate operand versus memory operand.
With short 8/16 or even 32 bit constants in general, immediate operands inside
the opcode are faster, rather than an additional memory read.
With 64-bit constants it is questionable and you may try both, as Bob suggested.
The opcode of mov/and... gets really huge, because all eight (or 2*4) immediate
bytes are coded inside it, an address requires only 4byte inside the opcode of
x86-32.
On the other hand with x86-64 in 64-bit mode addresses are eight bytes, so the
size aspects disappears with AMD64.
Anyway i would leave the #define and use it inside your const declaration.
And it makes sense to put often used oonstants in one context inside a structure
or inside an array. Then the memeory may addressed indirectly via some base
register/index resgister and small constant offsets which may be coded in one or
four bytes.
// with mapping a1=0 h1=7, a2=8, h8=63
#define FILEABB 0x0101010101010101ULL
const BitBoard fileAbb = FILEABB;
const BitBoard fileBitboards[8] =
{
FILEABB,
FILEBBB,
FILECBB,
FILEDBB,
FILEEBB,
FILEFBB,
FILEGBB,
FILEHBB,
};
If you use fileAbb or fileBitboards[0] doesn't matter, same code except the
address.
SIMD-instruction sets like MMX- or SSE2 don't offer any immediate operands at
all. But specially FILE-constants or their complements may be processed easily:
using pxor to set zero, pcmpeq to set -1 and to do bytewise psub of 0 - (-1),
ready is the FILEA-mask, other files require further subs or shift.
Gerd
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.