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diff --git a/ossintbas_content.rst b/ossintbas_content.rst new file mode 100644 index 0000000..acdd9b0 --- /dev/null +++ b/ossintbas_content.rst @@ -0,0 +1,245 @@ +DESCRIPTION +=========== + +OSS Integer BASIC is a BASIC interpreter from OSS, similar to BASIC XL +and BASIC XE. It was never released as a commercial product, and was +eventually released into the Public Domain. + +It appears to be complete and free of major bugs. There is no manual +for it, so I'm documenting the differences between Integer BASIC and +BASIC XL/XE here, as I discover them. + +For more info on the release:: + + https://forums.atariage.com/topic/257029-oss-d-day-part-3-integer-basic-source-code-now-in-pd/ + +NUMERICS +======== + +All numbers are signed 16-bit integers. There is no floating point support +at all. + +Two's complement is used, so bit 15 is the sign bit, and *-1* is +represented as *$FFFF*. + +The range is *-32768* to *32767*. Somewhat confusingly (but also +usefully), positive numbers in the range *32768* to *65535* can be +entered in program code, or as response to **INPUT**, etc... but when +they are **PRINT**\ed, they will appear as negative numbers. This +is unlike Apple's Integer BASIC, for instance. It was probably done +so that BASIC code could use the familiar memory locations. Example: +**PEEK(53279)** to read the console keys. It would be very annoying if +this had to be written as **PEEK(-12257)**\... although it does work +if written that way (Apple-style). + +Although floating point is not supported, it's possible to enter +numbers with a decimal point or even scientific notation. These will +silently be converted to integers, with rounding. If the result is +outside the range *-32768* to *65535*, you'll get an **ERROR- 3**. +This applies to numbers entered as part of the program as well as +those entered in response to **INPUT**, or **READ** from **DATA** +lines. + +COMMANDS +======== + +**VBLANKWAIT** + + Pause and wait for a vertical blank interrupt to occur. + + Abbreviation: **V.** + +**VINC** *<var>* + + Increment (add 1 to) a variable. This is about 30% faster than + **A=A+1**. Abbreviate as **VD.**. + + Abbreviation: **VI.** + +**VDEC** *<var>* + + Decrement (subtract 1 from) a variable. Abbreviate as **VD.**. + + Abbreviation: **VD.** + +**VCONST** *<num>*, *<var>* + + Add a constant to *var*. There are 8 constants, numbered 0 through + 7. They are set with the **SET** command, using arguments 16 to 23 + to set the constants. Example: **SET 16,10** sets constant 0 to 123, + and **VCONST 0,A** adds 10 to A. + + If *<num>* is greater than 7, the variable will be + unchanged. **SET** won't accept a number higher than 23 for its first + argument, so there'd be no way to set any constants other than 0 + to 7 anyway. + + When Integer BASIC first starts up, the constants are initialized + to what amounts to garbage values. You can examine them with + **SYS(16)** through **SYS(23)**, but it's a bad idea to depend on + them because the values are different between the disk and cartridge + versions of Integer BASIC. + + Using VCONST is about 15% faster than just adding a number to a + variable. + + Abbreviation: **VC.** + + +FUNCTIONS +========= + +**RUN(0)** + + Returns the run (coldstart) address of the interpreter. **? USR(RUN(0))** + restarts Integer BASIC. The *0* is a 'dummy' argument (ignored, like **FRE(0)**\). + +OPERATORS +========= + +**!** + + Binary OR. Infix operator. + +**&** + + Binary AND. Infix operator. + +**%** + + Binary exclusive OR (XOR). Infix operator. + +**<<** + + Left shift, like C. Infix operator. Result is the expression on the left, + shifted left by the number of bits on the right. Examples: **1<<4** + is 16, **255<<1** is 510. + + Bits shifted off the left end of the number are lost. Zeroes are + shifted in, for the low-order bit(s). Shifting anything left 16 times + results in zero. Since bit 15 is the sign bit, shifting a 1 into bit + 15 will result in a negative number. + +**>>** + + Right shift, like C. Infix operator. Result is the expression + on the left, shifted to the right, by the number of bits on the + right. Examples: **16>>4** is 1, **255>>1** is 127. + + Bits shifted off the right end of the number are lost. Zeroes are + shifted in, for the high-order bit(s). Shifting any negative number + to the right will result in a positive numbers, since a zero will be + shifted into the sigh bit. + +**^&** + + Binary NAND. Like AND, but inverts the bits in the result. Infix operator. + +**^!** + + Binary NOR. Infix operator. + +**^%** + + Binary NXOR. Infix operator. + +**\\** + + Modulus. Infix operator. Result of **X&Y** is the remainder of **X/Y**. + + *NOTE* that this is **broken** in the cartridge version of Integer BASIC, + though it works correctly in the disk version. See **BUGS**, below. + + +COMPATIBILITY +============= + +Integer BASIC can't LOAD programs that were SAVEd by any other BASIC, +and programs SAVEd by Integer BASIC can't be LOADed in any other +BASIC. Use LIST and ENTER instead. + +Actually, the disk and cartridge versions of Integer BASIC can't even +LOAD each others' programs. They use a different set of token numbers. +This is because the cartridge version includes the **HITCLR** command, +but the disk version does not. + +The **INT()** function exists in Integer BASIC, but it doesn't actually +do anything. Seems to be provided for compatibility with other BASICs. + +Missing Commands +---------------- + +Integer BASIC has the full command set of the BASIC XL cartridge, +minus these commands: + +**DEG** **RAD** **RGET** **RPUT** + +The cartridge version of Integer BASIC has the **HITCLR** command +(from BASIC XE), but the disk version does not. + +The BASIC XL extension disk commands (**LOCAL**, **EXIT**, +**PROCEDURE**, **CALL**, **SORTUP**, and **SORTDOWN**) don't exist in +Integer BASIC. If there was ever an extensions disk for Integer BASIC, +nobody's found it yet. + +The extra commands in BASIC XE (**EXTEND**, **INVERSE**, **NORMAL**, +**BLOAD**, and **BSAVE**) are not supported. + +Missing Operators/Functions +--------------------------- + +**^** + There is no exponentiation operator; **2^2** is a syntax error. + +**ATN()**, **CLOG()**, **COS()**, **EXP()**, **LOG()**, **SIN()** + There are no trigonometric functions in Integer BASIC. These can + be used as array variable names, if you wish. + +**USING** + BASIC XL and XE's "PRINT USING" doesn't exist in Integer BASIC. + +BUGS +==== + +Modulo Arithmetic +----------------- + +The **\\** (modulus) operator returns incorrect results in the +cartridge version of Integer BASIC. This program demonstrates the +bug:: + + 10 For I=1 To 10 + 20 ? I,I\3,I-(I/3)*3 + 30 Next I + +When run with the disk version, the results are correct:: + + 1 1 1 + 2 2 2 + 3 0 0 + 4 1 1 + 5 2 2 + 6 0 0 + 7 1 1 + 8 2 2 + 9 0 0 + 10 1 1 + +The same program run with the cartridge version gives:: + + 1 254 1 + 2 255 2 + 3 0 0 + 4 1 1 + 5 2 2 + 6 253 0 + 7 254 1 + 8 255 2 + 9 0 0 + 10 1 1 + +This is obviously wrong. + +If you're writing a real program in Integer BASIC, I recommend +avoiding the **\\** operator entirely. Write something like **X-X/Y\*Y** +instead. |