Vector Basic Interpreter Basic 80, Reference Manual, Page: 156 / 190

FAC-2 contains the middle 8 bits of mantissa and
FAC-1 contains the highest 7 bits of mantissa
with leading 1 suppressed (implied). Bit 7
is
the sign of the number (O=positive, 1-negative).
FAC
is
the exponent
minus
128, and the binary
point
is
to the left of the most significant
bit of the mantissa.
If ~e argument
is
a double precision floating point number:
FAC-7 through FAC-4 contain four more bytes
of mantissa (FAC-7 contains the lowest 8 bits).
If the
to 3
string
255).
8 bits
argument is a string, the [D,El register pair points
bytes called the "string descriptor." Byte 0 of the
descriptor contains the length of the string (0 to
Bytes 1 and 2, respectively, are the lower and upper
of the string starting address in string space.
CAUTION: If the argument is a string literal in the
program, the string descriptor will point to program text.
Be careful not to alter or destroy your program this way.
To avoid unpredictable results, add
+"
II
to the string
literal in the program. Example:
This will copy the string literal into string space and will
prevent alteration of program text during a subroutine call.
Usually, the value returned by a USR function
is
the same
type (integer, string, single precision or double precision)
as the argument that was passed to it. However, calling the
MAKINT routine returns the integer in [H,LJ as the value of
the function, forcing the value returned by the function to
be integer. To execute MAKINT, use the following sequence
to return from the subroutine:
POSH
LBLD
X'l'HL
H
xxx
1save value to be returned
1get address of MAKINT routine
;save return on stack and
;get back [H,Ll
1return
Also, the argument of the function, regardless of its type,
may be forced to an integer by callinq ~~e FRCINT routine to
get the integer value of the argument in [H,LJ. Execute the
following routine:
LXI
H ;get address
of subroutine
;continuation
PUSH H
;place on stack
\~.
LHLD
xxx ;get address
of FRCINT
PCHL
SUB1 :
• •
.
•
.