Technical information about Locomotive BASIC - Revision history

CPM User: /* BASIC GOSUB Subroutines */

2025-09-06T03:00:27Z

BASIC GOSUB Subroutines

← Older revision		Revision as of 03:00, 6 September 2025
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	If a BASIC game should issue a MEMORY FULL error, the easiest test is to say RETURN. If Unexpected RETURN doesn't occur and the code tries to continue, it will be a sign of Subroutines not being able to RETURN after a GOSUB ia issued. The easiest course is to remove Subroutines. A game for example may have a series of GOSUBs going to a line checking IF something is true, and if so GOTO somewhere else where a RETURN may not be found. In those situations a GOSUB should be replaced with an IF...THEN..[line number] thus removing the Subroutine.		If a BASIC game should issue a MEMORY FULL error, the easiest test is to say RETURN. If Unexpected RETURN doesn't occur and the code tries to continue, it will be a sign of Subroutines not being able to RETURN after a GOSUB ia issued. The easiest course is to remove Subroutines. A game for example may have a series of GOSUBs going to a line checking IF something is true, and if so GOTO somewhere else where a RETURN may not be found. In those situations a GOSUB should be replaced with an IF...THEN..[line number] thus removing the Subroutine.

	IF you wish to ~~konw~~ more about this please see my ~~ammended~~ correction of the [[Amstrad Action December 1990 Type-Ins\|Amstrad Action Issue 63 Type-Ins Game Madballs]]. The original game which was nicely coded, eventually ran into the problem of MEMORY FULL, though to fully reveal this error the game needed to be played for over 20 minutes. Another way to test for this error is to inspect the area of &AE8C to &B08B or &AE70 to &B06F depending on which version of BASIC is used.		If you wish to know more about this please see my amended correction of the [[Amstrad Action December 1990 Type-Ins\|Amstrad Action Issue 63 Type-Ins Game Madballs]]. The original game which was nicely coded, eventually ran into the problem of MEMORY FULL, though to fully reveal this error the game needed to be played for over 20 minutes. Another way to test for this error is to inspect the area of &AE8C to &B08B or &AE70 to &B06F depending on which version of BASIC is used.

	== BASIC tokens ==		== BASIC tokens ==

CPM User at 08:36, 27 August 2025

2025-08-27T08:36:12Z

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 #This data defines the tokenised BASIC program line and exists if the length of line data in bytes is not "0". The length is dependant on the BASIC program line contents.
 #This value defines the end of the tokenised BASIC line data and exists if the length of line data in bytes is not "0". The BASIC interpreter looks for this token during the processing of this line, and if found, will stop execution and continue to the next line.
 == BASIC tokens  ==

Arnoldemu: /* Sign */

2025-08-24T10:24:34Z

Sign

← Older revision		Revision as of 10:24, 24 August 2025
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	The sign is represented by bit 7 of byte 3. The value of the sign bit indicates the sign of the floating point number.		The sign is represented by bit 7 of byte 3. The value of the sign bit indicates the sign of the floating point number.

	#*If the sign bit is "1", then the number is negative.		*If the sign bit is "1", then the number is negative.
	#*If the sign bit is "0", then the number is positive.		*If the sign bit is "0", then the number is positive.

	=== Mantissa ===		=== Mantissa ===

Arnoldemu: /* Exponent */

2025-08-24T10:24:22Z

Exponent

← Older revision		Revision as of 10:24, 24 August 2025
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	The exponent is 8-bit and is stored in byte 4. It is stored with a bias of 128.		The exponent is 8-bit and is stored in byte 4. It is stored with a bias of 128.

	#*128-255 are positive exponents,		*128-255 are positive exponents,
	#*1-127 are negative exponents.		*1-127 are negative exponents.
	#*0 means, the number is zero		*0 means, the number is zero

	To obtain the signed exponent, you must subtract 128 from the stored exponent. The minimum exponent is 1 and this describes a number of 2^-127. The maximum exponent is 255 and this describes a number of 2^127.		To obtain the signed exponent, you must subtract 128 from the stored exponent. The minimum exponent is 1 and this describes a number of 2^-127. The maximum exponent is 255 and this describes a number of 2^127.

Arnoldemu: /* BASIC floating-point/real variables */

2025-08-24T10:24:05Z

BASIC floating-point/real variables

← Older revision		Revision as of 10:24, 24 August 2025
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	A floating point (real) variable describes a number with integer and fractional parts. The biggest figure which can be stored correctly in RAM by a variable is 2^32-1 = 4294967295.		A floating point (real) variable describes a number with integer and fractional parts. The biggest figure which can be stored correctly in RAM by a variable is 2^32-1 = 4294967295.

	#A real variable is defined with a "!" character postfix.		*A real variable is defined with a "!" character postfix.

	e.g.		e.g.
	<pre>a! = 3.141592654		<pre>a! = 3.141592654
	</pre>		</pre>
	#A real number uses 5 bytes of memory as storage. The format is described above.		*A real number uses 5 bytes of memory as storage. The format is described above.
	#The address of a real variable can be found in BASIC by:		*The address of a real variable can be found in BASIC by:
	<pre>PRINT @a!		<pre>PRINT @a!
	</pre>		</pre>

Arnoldemu: /* BASIC integer variables */

2025-08-24T10:23:52Z

BASIC integer variables

← Older revision		Revision as of 10:23, 24 August 2025
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	<br> NOTES:		<br> NOTES:

	#A integer variable is defined with a "%" character postfix.		*A integer variable is defined with a "%" character postfix.

	e.g.		e.g.
	<pre>a% = 3		<pre>a% = 3
	</pre>		</pre>
	#A integer variable has a range of -32768 to 32767		*A integer variable has a range of -32768 to 32767
	#A integer variable always uses two bytes of memory as storage with the following format:		*A integer variable always uses two bytes of memory as storage with the following format:

	{\| border="1"		{\| border="1"
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	\|}		\|}

	#The address of the integer variable can be found in BASIC by:		*The address of the integer variable can be found in BASIC by:
	<pre>PRINT @a%		<pre>PRINT @a%
	</pre>		</pre>

Arnoldemu: /* BASIC string variables */

2025-08-24T10:23:40Z

BASIC string variables

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	\|}		\|}

	*The address of the "string descriptor block" for the string variable can be found in BASIC by typing: <pre>PRINT @a$		*The address of the "string descriptor block" for the string variable can be found in BASIC by typing:
			<pre>PRINT @a$
	</pre>		</pre>

Arnoldemu: /* BASIC string variables */

2025-08-24T10:23:24Z

BASIC string variables

← Older revision		Revision as of 10:23, 24 August 2025
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	<br> NOTES:		<br> NOTES:

	#A string variable is defined in BASIC with a "$" character postfix.		*A string variable is defined in BASIC with a "$" character postfix.

	e.g.		e.g.

Arnoldemu: /* BASIC string variables */

2025-08-24T10:23:12Z

BASIC string variables

← Older revision		Revision as of 10:23, 24 August 2025
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	<pre>a$ = "hello"		<pre>a$ = "hello"
	</pre>		</pre>
	#A string variable is described internally by a "string descriptor block" which has the following structure:		*A string variable is described internally by a "string descriptor block" which has the following structure:

	{\| border="1"		{\| border="1"
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	\|}		\|}

	#The address of the "string descriptor block" for the string variable can be found in BASIC by typing: <pre>PRINT @a$		*The address of the "string descriptor block" for the string variable can be found in BASIC by typing: <pre>PRINT @a$
	</pre>		</pre>

	replacing "a$" with the name of the string variable.		replacing "a$" with the name of the string variable.

	#A string uses a minimum of 3 bytes of storage (a 0 character length string) and a maximum of 258 bytes of storage. 3 bytes are used by the "string descriptor block")		*A string uses a minimum of 3 bytes of storage (a 0 character length string) and a maximum of 258 bytes of storage. 3 bytes are used by the "string descriptor block")
	#A string variable can contain any ASCII character code in the range 0-255.		*A string variable can contain any ASCII character code in the range 0-255.
	#A string variable can store a minimum of 0 characters and a maximum of 255 characters.		*A string variable can store a minimum of 0 characters and a maximum of 255 characters.
	#The length of the string in characters is defined in the string descriptor block. The string does not have a termination character.		*The length of the string in characters is defined in the string descriptor block. The string does not have a termination character.

	[[Category:Programming]]		[[Category:Programming]]

Arnoldemu: /* BASIC integer variables */

2025-08-24T10:22:32Z

BASIC integer variables

← Older revision		Revision as of 10:22, 24 August 2025
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	\|}		\|}

	#The address of the integer variable can be found in BASIC by: <pre>PRINT @a%		#The address of the integer variable can be found in BASIC by:
			<pre>PRINT @a%
	</pre>		</pre>