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3.2 KiB
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50 lines
No EOL
3.2 KiB
Markdown
---
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title: Michael Abrash's Graphics Programming Black Book, Special Edition
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author: Michael Abrash
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date: '1997-07-01'
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isbn: '1576101746'
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publisher: The Coriolis Group
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category: 'Web and Software Development: Game Development,Web and Software Development:
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Graphics and Multimedia Development'
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chapter: '14'
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pages: 267-268
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---
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How fast *is* Boyer-Moore? Listing 14.1 is a C implementation of
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Boyer-Moore searching; Listing 14.2 is a test-bed program that searches
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up to the first 32K of a file for a pattern. Table 14.1 (all times
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measured with Turbo Profiler on a 20 MHz cached 386, searching a
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modified version of the text of this chapter) shows that this
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implementation is generally much slower than **REPNZ SCASB,** although
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it does come close when searching for long patterns. Listing 14.1 is
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designed primarily to make later assembly implemenmore comprehensible,
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rather than faster; Sedge's implementation uses arrays rather than
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pointers, is a great deal more compact and very clever, and may be
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somewhat faster. Regardless, the far superior performance of **REPNZ
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SCASB** clearly indicates that assembly language is in order at this
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point.
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| | "g;" | "Yogi" | "igoY" | "Adrian" | "Conclusion" | "You don't know what you know" |
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|--------------------------------------------------------------------|-------|--------|--------|----------|--------------|--------------------------------|
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| Searching approach | (16K) | (16K) | (16K) | (\<1K) | (16K) | (16K) |
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| REPNZ SCASB on first char a (Listing 9.1) | 8.2 | 7.5 | 9.7 | 0.4 | 7.4 | 8.1 |
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| REPNZ SCASB on least common char (Listing 9.2) | 7.6 | 7.5 | 7.5 | 0.5 | 7.5 | 7.5 |
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| Boyer-Moore in C (Listing 14.1) | 71.0 | 38.4 | 37.7 | 1.8 | 18.2 | 9.2 |
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| Standard Boyer-Moore in ASM (code not shown) | 38.5 | 21.0 | 20.5 | 0.8 | 9.4 | 4.8 |
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| Quick handling of first mismatch Boyer-Moore in ASM (Listing 14.3) | 14.1 | 8.9 | 7.7 | 0.4 | 4.0 | 2.0 |
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| \<=255 pattern length + sentinelBoyer-Moore in ASM (Listing 14.4) | 8.1 | 5.2 | 4.6 | 0.3 | 2.6 | 1.2 |
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Table: Table 14.1 Comparison of searching techniques.
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Search pattern (approximate distance searched before match is shown in
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parentheses).\
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Times are in milliseconds; shorter is better.
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The entry "Standard Boyer-Moore in ASM" in Table 14.1 refers to
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straight-forward hand optimization of Listing 14.1, code that is not
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included in this chapter for the perfectly good reason that it is slower
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in most cases than **REPNZ SCASB.** I say this casually now, but not so
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yesterday, when I had all but concluded that Boyer-Moore was simply
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inferior on the x86, due to two architectural quirks: the string
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instructions and slow branch. I had even coined a neat phrase for it:
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Architecture is destiny. Has a nice ring, doesn't it? |