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> Main > making a large lookup table |
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Borsuc 29 Jun 2009, 00:19
Fill it with what?
EDIT: by "quad words" you mean "english words with 4 characters" or "quadwords" ("word" is 16-bits number)? |
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29 Jun 2009, 00:19 |
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tthsqe 29 Jun 2009, 02:38
quad word = 64 bit integer
The look up table should look like [starting address ] = 0xFFFFFFFFFFFFFFFF [starting address + 8] = 0xFFFFFFFFFFFFFFFF [starting address +16] = 0xFFFFFFFFFFFFFFFF ... [starting address + bignum*8] I don't want the program to have a chance of overwriting anything that happens to be at these latter addresses. |
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29 Jun 2009, 02:38 |
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tthsqe 29 Jun 2009, 03:36
I think I got it:
table db 1000 dup (0,0,0,0,0,0,0,0) Will this set aside 1000 8-byte memory locations for table? Is there a better way to do this to allow for faster lookup times? |
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29 Jun 2009, 03:36 |
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sinsi 29 Jun 2009, 04:00
Code: table rq 1000 |
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29 Jun 2009, 04:00 |
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tthsqe 29 Jun 2009, 06:40
hm...
Code: table dq 1000 Code: table dq 1000 dup 0 |
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29 Jun 2009, 06:40 |
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sinsi 29 Jun 2009, 06:53
"rq", not "dq" - reserve quadword(s)
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29 Jun 2009, 06:53 |
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Borsuc 30 Jun 2009, 02:29
I'm confused. You said you wanted 0xFFFFFFFFFFFFFFFF, not 0, so why use dup(0) in your examples? Use dup(-1) instead.
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30 Jun 2009, 02:29 |
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bitRAKE 30 Jun 2009, 09:05
Code: table rq .size .size = 1000 . . macro table.init { lea rdi,[table] mov ecx,table.size or rax,-1 rep stosq } Code: lea rdi,[table] mov ecx,table.size * 8 mov al,-1 rep stosb |
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30 Jun 2009, 09:05 |
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tthsqe 02 Jul 2009, 02:31
Quote:
don't be confused. The intial contents of the table is irrelevent - it is initialized by the program and then used as a lookup table. |
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02 Jul 2009, 02:31 |
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tthsqe 02 Jul 2009, 02:38
If the start of the table is not a address that is a multiple of 8 (or 4?), will there be a penalty for misaligned memory accesses? Is there a way to fix this in fasm? The values are looked up in a performance sensitive loop.
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02 Jul 2009, 02:38 |
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LocoDelAssembly 02 Jul 2009, 02:56
If the memory access crosses a cache line boundary you'll get a penalty (not sure what about a misaligned access that doesn't crosses a line on newer processors). Since some elements in the table will obviously cross a cache line (and probably a page boundary too), it is better to align always.
Well, if what you want is a LUT of quad words then this is the way Code: align 8 ; Perhaps could be better to use 16, 32, or 64 (the latter is the cache line size of an Athlon64) LUT rq LUT_SIZE_IN_QWORDS |
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02 Jul 2009, 02:56 |
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