misc.txt

来自「汇编编程艺术」· 文本 代码 · 共 287 行

======================
Miscellaneous Routines
======================

This routines either defy categorization, or they haven't been properly
organized yet.

Mostly (like the rest of this library) they have simply been stuck here
until somebody gets the time to reorganize *everything*.




Routine:  Random
----------------

Author:		      Unknown.  Copied off a file on one of the networks,
		      tweaked, and added to the library.  Any info on the
		      original author would be appreciated.

Category:             Miscellaneous

Registers on entry:   None

Registers on return:  AX-	Contains random number

Flags affected:       None

Example of Usage:
			random	;Generate random number in AX
			puti	;Print the random number.


Description:    

 This routine computes a 16-bit random number each time you call it.  It
returns the random number in the AX register.  You may treat this as a signed
or unsigned value as it utilizes all 16 bits.  This code uses an internal
table of seed values.  If you are interested in producing repeatable sequences
of random numbers, please look at the source listings for this file.

 If you are interested in producing truly random values (well, closer than you
will get from this code by calling it right off the bat) look at the randomize
routine which tweaks the seed table based on the current time of day clock
value.

Include:	stdlib.a or misc.a


Routine:  Randomize
-------------------

Author:		      Unknown.  Copied off a file on one of the networks,
		      tweaked, and added to the library.  Any info on the
		      original author would be appreciated.

Category:             Miscellaneous

Registers on entry:   None

Registers on return:  None

Flags affected:       None

Example of Usage:
			randomize	;Randomize the seeds.
			random		;Get a brand new random number
			puti		;Print it

Description:    

Random's internal seed table is hard coded.  It was designed to produce a
sequence of random numbers with a very long period.  However, each time you
run a program using Random, it will generate the exact same sequence of
random numbers.  This could be distressing, for example, in a game where
after a while the player(s) could memorize some sequence of events based
on the random number generator.

 Randomize uses the time of day clock value to scramble the internal random
seed table.  If you call randomize before using random the first time, you
will generally get a different sequence of random numbers each time you
run the program.

 Note that it is dangerous to call randomize more than once inside any program.
The time of day clock is not a random source when invoked fairly often.
Furthermore, once the seeds are randomized, random does a pretty good job of
randomizing the results.

Include:	stdlib.a or misc.a


Routine:  cpuident
------------------

Author:		      Original implementation was supplied by Intel Corp.
		      Various modifications were made for inclusion into
		      the UCR Standard Library.

Category:             Miscellaneous

Registers on entry:   None

Registers on return:  AX-	Contains processor ID (86, 286, 386, or
				486.  Note 8088=86).

		      BX-	Contains coprocessor ID (87, 286, 387,
				or 487).  Note that a true 486 will have
				an 80487 built-in, 486sx chips, however, will
				not.

Flags affected:       None

Example of Usage:
			cpuident
			cmp	ax, 8086	;Is this an 8086?

Description:

For those programs which absolutely need to know the CPU in use, CPUIDENT
does a reasonable job (in DOS real mode) of figuring this out for you.  As
with all CPU identification routines, there are bound to be some problems
with this one when operating in protected mode. But for normal DOS appli-
cations it appears to work great.  This routine came straight from the
horse's mouth (Intel Corporation) so you can place a little more faith in
it than most that are floating around.  Intel's blessing doesn't guarantee
that this routine is perfect, though; always keep that in mind.

Include:	stdlib.a or misc.a


Routine:  Argc
--------------

Category:             Utility Routine

Registers on Entry:   None

Registers on Return:  CX-	Number of command line parameters

Flags Affected:       None


Example of Usage:
			print
			db	"There were ",0
			argc
			mov	ax, cx
			puti
			print
			db	" command line parameters here",cr,lf,0

Description:    This routine returns the number of command line para-
		meters on the DOS command line.  Note that strings enclosed
		in quotation marks or apostrophes are counted as a single
		command line parameter.


Include:              stdlib.a or misc.a


Routine:  Argv
--------------

Category:             Utility Routine

Registers on Entry:   AX-	Which parameter to grab (1..n).
		      PSP-	Global variable containing the DOS program
				segment prefix value.

Registers on Return:  ES:DI-	Pointer to string on heap containing the
				specified parameter (empty string if the
				parameter does not exist).

Flags Affected:       carry-	Set if malloc error.


Example of Usage:     
			mov	ax, 2
			argv
			print
			db	"The second command line parameter is ",0
			puts
			free

Description:    
 This routine returns a string containing the specified command line argument.
You must pass the position number of the argument in AX; this routine returns
the specified string on the heap with ES:DI pointing at the string.  Note that
the command line parameters are numbered starting from one.  If you specify an
out of range value, this routine returns a pointer to a zero byte (the empty
string).


Include:              stdlib.a or misc.a


Routine:  GetEnv
----------------

Category:             Utility Routine

Registers on Entry:   ES:DI-	Points at a string containing the name of
				the environment variable you want to find.
		      PSP-	Global variable containing the DOS program
				segment prefix value.

Registers on Return:  ES:DI-	Pointer to string in the environment space
				containing the characters immediately after
				the name of the environment variable in the
				environment string space.

Flags Affected:       carry-	Set if malloc error.


Example of Usage:     
			les	di, EnvVarStrPtr
			getenv
			print
			db	"The value of the environment variable is ",0
			puts
			free

Description:    

  This routine returns a pointer to the first characters following an
environment variable in the program's environment variable space.  It points
at the very first character following the name, so it typically points at
an equal sign (e.g., the PATH environment variable is typically of the form
"PATH=xxxxxxxx" and the "=" is the first char past the name).  If this routine
does not find the specified environment variable, it returns a pointer to
a single zero byte.  Since the pointer is in the environment space, you should
not store anything at this address.  Instead, first copy the string with STRDUP
if you need to modify it.

Include:              stdlib.a or misc.a


Routine:  DOS
-------------

Category:             Utility Routine

Registers on Entry:   AH-	DOS opcode

Registers on Return:  Depends on particular DOS call

Flags Affected:       Depends on DOS call.


Example of Usage:     
			mov	ah, 9
			DOS
			 .
			 .
			 .
			DOS	7
Description:    

  This macro invokes DOS via the INT 21h interrupt.  If there is no parameter
to the macro, it simply issues the INT 21h instruction.  If a parameter is
present, it emits "mov ah, operand" followed by the INT 21h instruction.

Include:              stdlib.a or consts.a


Routine:  ExitPgm
-----------------

Category:             Utility Routine

Registers on Entry:  None

Registers on Return:  Doesn't return

Flags Affected:       N/A


Example of Usage:
			ExitPgm
Description:

  This macro exits the program and returns to DOS.

Include:              stdlib.a or consts.a