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This commit is contained in:
James Gregory 2013-12-30 18:34:31 +11:00
commit 18011c595a
352 changed files with 6040 additions and 6040 deletions
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32
07-03.md
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@ -14,21 +14,21 @@
.data
; Sample string to search through.
SampleString labelbyte
db ‘This is a sample string of a long enough length ’
db ‘so that raw searching speed can outweigh any ’
db ‘extra set-up time that may be required.’,0
db ‘This is a sample string of a long enough length '
db ‘so that raw searching speed can outweigh any '
db ‘extra set-up time that may be required.',0
SAMPLE_STRING_LENGTH equ $-SampleString
; User prompt.
Prompt db ‘Enter character to search for:$’
Prompt db ‘Enter character to search for:$'
; Result status messages.
ByteFoundMsg db 0dh,0ah
db ‘Specified byte found.’,0dh,0ah,‘$’
db ‘Specified byte found.',0dh,0ah,‘$'
ZeroByteFoundMsg db 0dh, 0ah
db ‘Zero byte encountered.’,0dh,0ah,‘$’
db ‘Zero byte encountered.',0dh,0ah,‘$'
NoByteFoundMsg db 0dh,0ah
db ‘Buffer exhausted with no match.’, 0dh, 0ah, ‘$’
db ‘Buffer exhausted with no match.', 0dh, 0ah, ‘$'
.code
Startprocnear
@ -45,12 +45,12 @@
call SearchMaxLength ;search the buffer
mov dx,offset ByteFoundMsg ;assume we found the byte
jc PrintStatus ;we did find the byte
;we didn’t find the byte, figure out
;we didn't find the byte, figure out
;whether we found a zero byte or
;ran out of buffer
mov dx,offset NoByteFoundMsg
;assume we didn’t find a zero byte
jcxz PrintStatus ;we didn’t find a zero byte
;assume we didn't find a zero byte
jcxz PrintStatus ;we didn't find a zero byte
mov dx,offset ZeroByteFoundMsg ;we found a zero byte
PrintStatus:
mov ah,9 ;DOS print string function
@ -79,18 +79,18 @@
SearchMaxLengthLoop:
lodsb ;get the next byte
cmp al,ah ;is this the byte we want?
jz ByteFound ;yes, we’re done with success
jz ByteFound ;yes, we're done with success
and al,al ;is this the terminating 0 byte?
jz ByteNotFound ;yes, we’re done with failure
loop SearchMaxLengthLoop ;it’s neither, so check the next
jz ByteNotFound ;yes, we're done with failure
loop SearchMaxLengthLoop ;it's neither, so check the next
;byte, if any
ByteNotFound:
clc ;return “not found” status
clc ;return "not found" status
ret
ByteFound:
dec si ;point back to the location at which
;we found the searched-for byte
stc ;return “found” status
stc ;return "found" status
ret
SearchMaxLengthendp
end Start
@ -102,7 +102,7 @@ bytes are checked for each **LOOP** performed. The same instructions are
used inside the loop in each listing, but Listing 7.2 is arranged so
that three-quarters of the **LOOP**s are eliminated. Listings 7.1 and
7.2 perform exactly the same task, and they use the same instructions in
the loop—the searching algorithm hasn’t changed in any way—but we have
the loop—the searching algorithm hasn't changed in any way—but we have
sequenced the instructions differently in Listing 7.2, and that makes
all the difference.