The BBC and Master Computer Public Domain Library

B2EC ENVELOPE

Submitted by Steve Fewell

Description:

Get the result of the expression at BASIC Text Pointer A and convert the result to Integer (if Float), or issue a
'Type mismatch' error (if String value found).
Set X to 13 (as we have 14 parameters to obtain).

Loop for X number of times. For each loop:

* Push the Integer result (next parameter) LSB (&2A) to the Stack.

* Temporarily push X to the stack

* Check for "," (comma) charater (issue "Missing ," error if not found), and get the Integer result of expression at
     BASIC Text pointer B.

* Retrieve X from the stack.

* Decrement X value.

* If X is not 0 yet then loop again.

Now, we have the first 13 parameters on the stack and the last parameter in the IWA (&2A).

Call routine &9B96 to check that the Statement terminates correctly (if not, then a 'Syntax' error is issued).
Store the last parameter (IWA location &2A) in location &44.
Set X to 12 (Number of parameters left - 1).
Set Y to 8 (OSWORD call number for ENVELOPE).

[&B307] Pop the last Byte from the stack and store in location (&37 + X), i.e. location &43 for the 13th parameter).
Decrement X and keep repeating from &B307 until X is negative.

Now location &37 to location &37 + Original X value + 1 (i.e. &44 for ENVELOPE parameter block) contain the
OSWORD call parameters.
Set A to Y value (the number of the OSWORD call).
Set X to #&37 and Y to #&00 (as the start of the parameter block is &0037).
Call the Operating System OSWORD routine (&FFF1) to perform the required operation.
Jump to &9005 to start processing the next Statement (if any).

Disassembly for the ENVELOPE routine

B2EC	o	032 111 146	20 6F 92	JSR &926F Evaluate Expression at BASIC Text pointer A & convert result to integer
B2EF		162 013	A2 0D	LDX#&0D
B2F1	*	165 042	A5 2A	LDA &2A
B2F3	H	072	48	PHA
B2F4		218	DA	PHX
B2F5		032 172 150	20 AC 96	JSR &96AC Check for ',', get result of expression and convert result to Integer
B2F8		250	FA	PLX
B2F9		202	CA	DEX
B2FA		208 245	D0 F5	BNE -11 --> &B2F1
B2FC		032 150 155	20 96 9B	JSR &9B96 Check for end of Statement (PTR B)
B2FF	*	165 042	A5 2A	LDA &2A
B301	D	133 068	85 44	STA &44
B303		162 012	A2 0C	LDX#&0C
B305		160 008	A0 08	LDY#&08
B307	h	104	68	PLA
B308	7	149 055	95 37	STA &37,X
B30A		202	CA	DEX
B30B		016 250	10 FA	BPL -6 --> &B307
B30D		152	98	TYA
B30E	7	162 055	A2 37	LDX#&37
B310		160 000	A0 00	LDY#&00
B312		032 241 255	20 F1 FF	JSR &FFF1 OSWORD
B315		128 011	80 0B	BRA 11 --> &B322 [JMP &9005] Continue with next Statement

 

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