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James Gregory
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352 changed files with 6040 additions and 6040 deletions
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07-04.md
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07-04.md
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@ -13,21 +13,21 @@
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.data
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; Sample string to search through.
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SampleStringlabelbyte
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db ‘This is a sample string of a long enough length ’
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db ‘so that raw searching speed can outweigh any ’
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db ‘extra set-up time that may be required.’,0
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db ‘This is a sample string of a long enough length '
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db ‘so that raw searching speed can outweigh any '
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db ‘extra set-up time that may be required.',0
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SAMPLE_STRING_LENGTH equ $-SampleString
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; User prompt.
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Prompt db ‘Enter character to search for:$’
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Prompt db ‘Enter character to search for:$'
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; Result status messages.
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ByteFoundMsg db 0dh,0ah
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db ‘Specified byte found.’,0dh,0ah,‘$’
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db ‘Specified byte found.',0dh,0ah,‘$'
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ZeroByteFoundMsg db 0dh,0ah
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db ‘Zero byte encountered.’, 0dh, 0ah, ‘$’
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db ‘Zero byte encountered.', 0dh, 0ah, ‘$'
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NoByteFoundMsg db 0dh,0ah
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db ‘Buffer exhausted with no match.’, 0dh, 0ah, ‘$’
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db ‘Buffer exhausted with no match.', 0dh, 0ah, ‘$'
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; Table of initial, possibly partial loop entry points for
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; SearchMaxLength.
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@ -52,12 +52,12 @@
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call SearchMaxLength ;search the buffer
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mov dx,offset ByteFoundMsg ;assume we found the byte
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jc PrintStatus ;we did find the byte
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;we didn’t find the byte, figure out
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;we didn't find the byte, figure out
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;whether we found a zero byte or
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;ran out of buffer
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mov dx,offset NoByteFoundMsg
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;assume we didn’t find a zero byte
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jcxz PrintStatus ;we didn’t find a zero byte
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;assume we didn't find a zero byte
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jcxz PrintStatus ;we didn't find a zero byte
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mov dx,offset ZeroByteFoundMsg ;we found a zero byte
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PrintStatus:
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mov ah,9 ;DOS print string function
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@ -99,36 +99,36 @@
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SearchMaxLengthEntry4:
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lodsb ;get the next byte
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cmp al,ah ;is this the byte we want?
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jz ByteFound ;yes, we’re done with success
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jz ByteFound ;yes, we're done with success
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and al,al ;is this the terminating 0 byte?
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jz ByteNotFound ;yes, we’re done with failure
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jz ByteNotFound ;yes, we're done with failure
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SearchMaxLengthEntry3:
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lodsb ;get the next byte
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cmp al,ah ;is this the byte we want?
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jz ByteFound ;yes, we’re done with success
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jz ByteFound ;yes, we're done with success
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and al,al ;is this the terminating 0 byte?
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jz ByteNotFound ;yes, we’re done with failure
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jz ByteNotFound ;yes, we're done with failure
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SearchMaxLengthEntry2:
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lodsb ;get the next byte
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cmp al,ah ;is this the byte we want?
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jz ByteFound ;yes, we’re done with success
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jz ByteFound ;yes, we're done with success
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and al,al ;is this the terminating 0 byte?
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jz ByteNotFound ;yes, we’re done with failure
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jz ByteNotFound ;yes, we're done with failure
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SearchMaxLengthEntry1:
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lodsb ;get the next byte
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cmp al,ah ;is this the byte we want?
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jz ByteFound ;yes, we’re done with success
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jz ByteFound ;yes, we're done with success
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and al,al ;is this the terminating 0 byte?
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jz ByteNotFound ;yes, we’re done with failure
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loop SearchMaxLengthLoop ;it’s neither, so check the next
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jz ByteNotFound ;yes, we're done with failure
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loop SearchMaxLengthLoop ;it's neither, so check the next
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; four bytes, if any
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ByteNotFound:
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clc ;return “not found” status
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clc ;return "not found" status
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ret
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ByteFound:
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dec si ;point back to the location at which
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; we found the searched-for byte
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stc ;return “found” status
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stc ;return "found" status
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ret
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SearchMaxLengthendp
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end Start
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@ -136,11 +136,11 @@
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How much difference? Listing 7.2 runs in 121 µs—40 percent faster than
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Listing 7.1, even though Listing 7.2 still uses **LOOP** rather than
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**DEC CX/JNZ.** (The loop in Listing 7.2 could be unrolled further, too;
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it’s just a question of how much more memory you want to trade for
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ever-decreasing performance benefits.) That’s typical of local
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optimization; it won’t often yield the order-of-magnitude improvements
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it's just a question of how much more memory you want to trade for
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ever-decreasing performance benefits.) That's typical of local
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optimization; it won't often yield the order-of-magnitude improvements
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that algorithmic improvements can produce, but it can get you a critical
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50 percent or 100 percent improvement when you’ve exhausted all other
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50 percent or 100 percent improvement when you've exhausted all other
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avenues.
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------------------- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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