The floating point package reference

The floating point package (hereinafter referred to as the FPP) uses a different RST call from the main system calls, the format of a floating point call is as follows:

RST $18 DEFB <function code>

so apart from the different restart number, much the same as the OS calls. In the text we will assume a macro has been defined and use the following:

FPP <function mnemonic>

Parameters are passed to and from the FPP in a rather bizarre collection of registers. The main register group is HLhlC (remember, lower case for alternate set), and where a second parameter is required it is passed in DEdeB. These divide into mantissa and exponent as follows:

Parameter 1	Parameter 2	Significance

Parameter 1	Parameter 2	Significance
H	D	Most significant byte of mantissa
L	E
h	d
l	e	Least significant byte of mantissa
C	B	Exponent byte

There are certain exceptions, which are explained where relevant (for instance one operation returns the numeric value of a string, so takes a pointer to the string in HL as its parameter). Here is the full list of parameter bytes and the FPP functions which they invoke. First number is the index number of the operation for FP_BAS. Second number is the RST 18H function code:

Mnemonic	Function Index Number	Function Code	Functionality	Description

Mnemonic	Function Index Number	Function Code	Functionality	Description
FP_AND	0	$21	`Bitwise logical AND`	(Integer only) Input parameters in HLhlC and DEdeB. Result in HLhlC.
FP_IDV	1	$24	`Quotient after division`	(Integer only) Input parameters in HLhlC and DEdeB (returns HLhlC / DEdeB). Result in HLhlC.
FP_EOR	2	$27	`Bitwise logical excusive OR`	(Integer only) Input parameters in HLhlC and DEdeB. Result in HLhlC.
FP_MOD	3	$2A	`Remainder after division`	(Integer only) Input parameters in HLhlC and DEdeB (returns the remainder of HLhlC / DEdeB). Result in HLhlC.
FP_OR	4	$2D	`Bitwise logical OR`	(Integer only) Input parameters in HLhlC and DEdeB. Result in HLhlC.
FP_LEQ	5	$30	`Test for less than or equal to`	Input parameters in HLhlC and DEdeB (test is HLhlC <= DEdeB). Result in HLhlC (-1 for TRUE; 0 for FALSE).
FP_NEQ	6	$33	`Test for not equal to`	Input parameters in HLhlC and DEdeB. Result in HLhlC (-1 for TRUE; 0 for FALSE).
FP_GEQ	7	$36	`Test for greater than or equal to`	Input parameters in HLhlC and DEdeB (test is HLhlC >= DEdeB). Result in HLhlC (-1 for TRUE; 0 for FALSE).
FP_LT	8	$39	`Test for less than`	Input parameters in HLhlC and DEdeB (test is HLhlC < DEdeB). Result in HLhlC (-1 for TRUE; 0 for FALSE).
FP_EQ	9	$3C	`Test for equality`	Input parameters in HLhlC and DEdeB. Result in HLhlC (-1 for TRUE; 0 for FALSE).
FP_MUL	10	$3F	`Multiplication`	Input parameters in HLhlC and DEdeB. Result in HLhlC.
FP_ADD	11	$42	`Addition`	Input parameters in HLhlC and DEdeB. Result in HLhlC.
FP_GT	12	$45	`Test for greater than`	Input parameters in HLhlC and DEdeB (test is HLhlC > DEdeB). Result in HLhlC (-1 for TRUE; 0 for FALSE).
FP_SUB	13	$48	`Subtraction`	Input parameters in HLhlC and DEdeB (returns HLhlC - DEdeB). Result in HLhlC.
FP_PWR	14	$4B	`Raise to power`	Input parameters in HLhlC and DEdeB (returns HLhlC ^ DEdeB). Result in HLhlC.
FP_DIV	15	$4E	`Division`	Input parameters in HLhlC and DEdeB (returns HLhlC / DEdeB). Result in HLhlC.
FP_ABS	16	$51	`Magnitude (ABSolute value)`	Input parameters in HLhlC. Result in HLhlC.
FP_ACS	17	$54	`Inverse cosine (Arc CoSine)`	Input parameters in HLhlC. Result in HLhlC, in radians.
FP_ASN	18	$57	`Inverse sine (Arc SiNe)`	Input parameters in HLhlC. Result in HLhlC, in radians.
FP_ATN	19	$5A	`Inverse tangent (Arc TaNgent)`	Input parameters in HLhlC. Result in HLhlC, in radians.
FP_COS	20	$5D	`Cosine`	Input parameters in HLhlC, in radians. Result in HLhlC.
FP_DEG	21	$60	`Convert radians to degrees`	Input parameters in HLhlC, in radians. Result in HLhlC, in degrees.
FP_EXP	22	$63	`Exponentiation`	Raise 'e' [2.718...] to power of. Input parameters in HLhlC. Result in HLhlC.
FP_INT	23	$66	`Integer truncation`	(floor truncation, not rounding) Input parameters in HLhlC. Result in HLhlC.
FP_LN	24	$69	`Natural logarithm`	(Naperian or base 'e') Input parameters in HLhlC. Result in HLhlC.
FP_LOG	25	$6C	`Common (base 10) logarithm`	Input parameters in HLhlC. Result in HLhlC.
FP_NOT	26	$6F	`Bitwise logical NOT`	(Integer only) Input parameters in HLhlC. Result in HLhlC.
FP_RAD	27	$72	`Convert degrees to radians`	Input parameters in HLhlC, in degrees. Result in HLhlC, in radians.
FP_SGN	28	$75	`Sign (signum)`	Input parameters in HLhlC. Result in HLhlC.
FP_SIN	29	$78	`Sine`	Input parameters in HLhlC, in radians. Result in HLhlC.
FP_SQR	30	$7B	`Square root`	Input parameters in HLhlC. Result in HLhlC.
FP_TAN	31	$7E	`Tangent`	Input parameters in HLhlC, in radians. Result in HLhlC.
FP_ZER	32	$81	`Return the constant zero`	(as an integer) Input irrelevant. Result in HLhlC (all zero).
FP_ONE	33	$84	`Return the floating point constant 1`	Input irrelevant. Result in HLhlC (HL=hl=0, C=$80)
FP_TRU	34	$87	`Return the integer constant -1`	Input irrelevant. Result in HLhlC (HL=hl=$FFFF, C=$00)
FP_PI	35	$8A	`Returns pi`	(the floating point representation of pi) Input irrelevant. Result in HLhlC.
FP_VAL	36	$8D	`Returns the numeric value of a string`	HL points to start of string (null-terminated). Result in HLhlC, and DE points to last character read; if the call succeeded, this will be the terminator byte. If the call failed, HLhlC = 0.
FP_STR	37	$90	`Return string representation of number`	Number to convert to string, in in HLhlC. DE points to space to insert string. DE points to character after string when call returns. The de (alternate) register pair contains a format control variable which has the effect of the two middle bytes of the BBC BASIC format control variable @%: The contents of e determine the maximum number of digits (ie. number of characters apart from decimal point or 'E') to be printed. The allowed range of values depends on the format selected (see below): General format Exponential format: 1-255 (leading zeros added beyond the 10th significant figure). Fixed format: 0-10 (in this case the number of digits printed after the decimal point). The contents of d determine the format of the resultant string for a given number; the options are: d=0: General format Integers are printed without a decimal point or exponent. Numbers between 0.1 and 1 will be printed with a decimal point but no exponent. Numbers less than 0.1 will be printed with a decimal point and exponent. Numbers greater than 1 will be printed without exponent unless this would involve more digits than allowed by the contents of the 'e' register (se above), and outside this range, will be printed with an exponent. d=1: Exponential format All numbers printed in exponential notation, eg. 1.0E0. d=2: Fixed format All numbers are printed with a fixed number of decimal places.
FP_FIX	38	$93	`Round a number to integer`	Input parameters in HLhlC (the call has no effect with C=0). Result in HLhlC.
FP_FLT	39	$96	`Convert from integer to floating point`	Input parameters in HLhlC (the call has no effect with C<>0). Result in HLhlC.
FP_TST	40	$99	`Test a number for zero and sign`	Input parameters in HLhlC. Result in A (0 for zero; $40 for positive; $C0 for negative).
FP_CMP	41	$9C	`Compare two numeric values`	Input parameters in HLhlC (left) and DEdeB (right). Result in A: 0 if HLhlC = DEdeB. $40 if HLhlC > DEdeB. $C0 if HLhlC < DEdeB.
FP_NEG	42	$9F	`Negate number, ie. result = -input`	Input parameters in HLhlC. Result in HLhlC.
FP_BAS		$A2	`Execute operation using index number`	Perform one of the above functions using the operation index number in A, eg.: `ld a, 33` `fpp FP_BAS` should call FP_ONE and return 1 (floating point). This facility can be useful if the operation depends on some parameter, to avoid writing selfmodifying code.