---
title: Michael Abrash's Graphics Programming Black Book, Special Edition
author: Michael Abrash
date: '1997-07-01'
isbn: '1576101746'
publisher: The Coriolis Group
category: 'Web and Software Development: Game Development,Web and Software Development:
  Graphics and Multimedia Development'
chapter: '14'
pages: 267-268
---

How fast *is* Boyer-Moore? Listing 14.1 is a C implementation of
Boyer-Moore searching; Listing 14.2 is a test-bed program that searches
up to the first 32K of a file for a pattern. Table 14.1 (all times
measured with Turbo Profiler on a 20 MHz cached 386, searching a
modified version of the text of this chapter) shows that this
implementation is generally much slower than **REPNZ SCASB,** although
it does come close when searching for long patterns. Listing 14.1 is
designed primarily to make later assembly implemenmore comprehensible,
rather than faster; Sedge's implementation uses arrays rather than
pointers, is a great deal more compact and very clever, and may be
somewhat faster. Regardless, the far superior performance of **REPNZ
SCASB** clearly indicates that assembly language is in order at this
point.

|                                                                    | "g;"  | "Yogi" | "igoY" | "Adrian" | "Conclusion" | "You don't know what you know" |
|--------------------------------------------------------------------|-------|--------|--------|----------|--------------|--------------------------------|
| Searching approach                                                 | (16K) | (16K)  | (16K)  | (\<1K)   | (16K)        | (16K)                          |
| REPNZ SCASB on first char a (Listing 9.1)                          | 8.2   | 7.5    | 9.7    | 0.4      | 7.4          | 8.1                            |
| REPNZ SCASB on least common char (Listing 9.2)                     | 7.6   | 7.5    | 7.5    | 0.5      | 7.5          | 7.5                            |
| Boyer-Moore in C (Listing 14.1)                                    | 71.0  | 38.4   | 37.7   | 1.8      | 18.2         | 9.2                            |
| Standard Boyer-Moore in ASM (code not shown)                       | 38.5  | 21.0   | 20.5   | 0.8      | 9.4          | 4.8                            |
| Quick handling of first mismatch Boyer-Moore in ASM (Listing 14.3) | 14.1  | 8.9    | 7.7    | 0.4      | 4.0          | 2.0                            |
| \<=255 pattern length + sentinelBoyer-Moore in ASM (Listing 14.4)  | 8.1   | 5.2    | 4.6    | 0.3      | 2.6          | 1.2                            |

Table: Table 14.1 Comparison of searching techniques.

Search pattern (approximate distance searched before match is shown in
parentheses).\
 Times are in milliseconds; shorter is better.

The entry "Standard Boyer-Moore in ASM" in Table 14.1 refers to
straight-forward hand optimization of Listing 14.1, code that is not
included in this chapter for the perfectly good reason that it is slower
in most cases than **REPNZ SCASB.** I say this casually now, but not so
yesterday, when I had all but concluded that Boyer-Moore was simply
inferior on the x86, due to two architectural quirks: the string
instructions and slow branch. I had even coined a neat phrase for it:
Architecture is destiny. Has a nice ring, doesn't it?