salloc.7

UNIX v6源代码 这几乎是最经典的unix版本 unix操作系统设计和莱昂氏unix源代码分析都是用的该版

.th SALLOC VII 6/15/72
.sh NAME
salloc \*- string allocation and manipulation
.sh SYNOPSIS
.nf
(get size in r0)
.bd "jsr	pc,allocate"
(header address in r1)
.s3
(get source header address in r0,
destination header address in r1)
.bd "jsr	pc,copy"
.s3
.bd "jsr	pc,wc"
.s3
(all following routines assume r1 contains header address)
.s3
.bd "jsr	pc,release"
.s3
(get character in r0)
.bd "jsr	pc,putchar"
.s3
.bd "jsr	pc,lookchar"
(character in r0)
.s3
.bd "jsr	pc,getchar"
(character in r0)
.s3
(get character in r0)
.bd "jsr	pc,alterchar"
.s3
(get position in r0)
.bd "jsr	pc,seekchar"
.s3
.bd "jsr	pc,backspace"
(character in r0)
.s3
(get word in r0)
.bd "jsr	pc,putword"
.s3
.bd "jsr	pc,lookword"
(word in r0)
.s3
.bd "jsr	pc,getword"
(word in r0)
.s3
(get word in r0)
.bd "jsr	pc,alterword"
.s3
.bd "jsr	pc,backword"
(word in r0)
.s3
.bd "jsr	pc,length"
(length in r0)
.s3
.bd "jsr	pc,position"
(position in r0)
.s3
.bd "jsr	pc,rewind"
.s3
.bd "jsr	pc,create"
.s3
.bd "jsr	pc,fsfile"
.s3
.bd "jsr	pc,zero"
.fi
.sh DESCRIPTION
This package is a complete set of routines
for dealing with almost arbitrary
length strings of words and bytes.
It lives in
.it /lib/libs.a.
The strings are stored on a disk file, so the sum of
their lengths can be considerably larger than
the available core.
A small buffer cache makes for reasonable speed.
.s3
For each string there is a header of four words, namely
a write pointer, a read pointer and pointers to the beginning and end of
the block containing the string.
Initially the read and write pointers point to the beginning of the string.
All routines that refer to a string require the header address in r1.
Unless the string is destroyed by the call,
upon return r1 will point to the same string, although
the string may have grown to the extent that it had to be
be moved.
.s3
.it Allocate
obtains a string of the requested size and returns
a pointer to its header in r1.
.s3
.it Release
releases a string back to free storage.
.s3
.it Putchar
and
.it putword
write a byte or word respectively into the string
and advance the write pointer.
.s3
.it Lookchar
and
.it lookword
read
a byte or word respectively from the string but do not advance the read pointer.
.s3
.it Getchar
and
.it getword
read a byte or word respectively from the string and advance the read pointer.
.s3
.it Alterchar
and
.it alterword
write a byte or word respectively into the string where the read pointer
is pointing and advance the read pointer.
.s3
.it Backspace
and
.it backword
read the last byte or word written and decrement the write pointer.
.s3
All write operations will automatically get a larger block if the current block is exceeded.
All read operations return with the error bit set if attempting to read beyond the write pointer.
.s3
.it Seekchar
moves the read pointer to the offset specified in r0.
.s3
.it Length
returns the current length of the string (beginning pointer to write pointer) in r0.
.s3
.it Position
returns the current offset of the read pointer in r0.
.s3
.it Rewind
moves the read pointer to the beginning of the string.
.s3
.it Create
returns the read and write pointers to the beginning of the string.
.s3
.it Fsfile
moves the read pointer to the current position of the write pointer.
.s3
.it Zero
zeros the whole string and sets the write pointer to the beginning of the string.
.s3
.it Copy
copies the string whose header pointer is in r0 to the string whose header pointer is in
r1.
Care should be taken in using the copy instruction since r1 will be changed if the contents of the source string
is bigger than the destination string.
.s3
.it Wc
forces the contents of the internal buffers and the header blocks to be written on disc.
.s3
An in-core version of this allocator exists in
.it dc
(I),
and a permanent-file version exists in
.it form
and 
.it fed
(VI).
.sh FILES
.if t .ta 1i
.if n .ta 13
/lib/libs.a	library, accessed by
.it "ld ... -ls"
.br
alloc.d	temporary file for string storage
.sh "SEE ALSO"
alloc (III)
.sh DIAGNOSTICS
`error in copy' \*- disk write error encountered in
.it copy.
.br
`error in allocator' \*- routine called with bad header pointer.
.br
`cannot open output file' \*- temp file 
.it alloc.d 
cannot be created or opened.
.br
`out of space' \*- no sufficiently large block or no 
header is available for a new or growing block.
.sh BUGS