ZX Spectrum Calculator literals
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00 jump-true  Jump if the top item is non-zero.
   dest-$

01 exchange   Top two items on the stack are swapped.

02 delete     Delete top item

Binary operations - replace top two items with result
-----------------------------------------------------
03 subtract   X - Y    (2nd item) - (top item)
04 multiply   X * Y    (2nd item) * (top item)
05 division   X / Y    (2nd item) / (top item)
06 to-power   X ^ Y    (2nd item) ^ (top item)
07 or         X OR Y   (2nd item) OR (top item)
08 no-&-no    X AND Y  (2nd item) AND (top item)   10 str-&-no    X$ AND Y   (2nd item) AND (top item)
09 no-l-eql   X <= Y   (2nd item) <= (top item)    11 str-l-eql   X$ <= Y$   (2nd item) <= (top item)
0A no-gr-eq   X >= Y   (2nd item) >= (top item)    12 str-gr-eq   X$ >= Y$   (2nd item) >= (top item)
0B nos-neql   X <> Y   (2nd item) <> (top item)    13 strs-neql   X$ <> Y$   (2nd item) <> (top item)
0C no-grtr    X > Y    (2nd item) > (top item)     14 str-grtr    X$ > Y$    (2nd item) > (top item)
0D no-less    X < Y    (2nd item) < (top item)     15 str-less    X$ < Y$    (2nd item) < (top item)
0E nos-eql    X = Y    (2nd item) = (top item)     16 strs-eql    X$ = Y$    (2nd item) = (top item)
0F addition   X + Y    (2nd item) + (top item)     17 strs-add    X$ + Y$    (2nd item) + (top item)

Uniary operations - replace top item with result
------------------------------------------------
18 val$       VAL$   Convert string to calculated string
19 usr-$      USR    Calculate address of user graphic character.
1A read-in    INKEY  INKEY$#n to read character from stream n.
1B negate     -      Negate top item
1C code       CODE   Convert string to character code.
1D val        VAL    Convert string to number.
1E len        LEN    Convert string to length of string.
1F sin        SIN    Calculate SIN n.
20 cos        COS    Calculate COS n.
21 tan        TAN    Calculate TAN n.
22 asn        ASN    Calculate ASN n.
23 acs        ACS    Calculate ACS n.
24 atn        ATN    Calculate ATN n.
25 ln         LN     Use series generator to calculate LN n.
26 exp        EXP    Use series generator to calculate EXP n.
27 int        INT    Round down to integer value.
28 sqr        SQR    Calculate square root.
29 sgn        SGN    Get sign of top item.
2A abs        ABS    Get absolute value of top item.
2B peek       PEEK   Read byte from memory.
2C in         IN     IN A,(C) to read from I/O port.
2D usr-no     USR    Call machine code.
2E str$       STR$   Convert number to string.  
2F chr$       CHR$   Convert number to character.
30 not        NOT    Replace top item with 1 if it is zero, otherwise replace with zero.

Misc. operations
----------------
31 duplicate         Duplicate the top item.

32 n-mod-m           (2nd item) MOD (top item), returning INT (N/M) at top of
                     stack and N-INT(N/M) as a calculated MOD as 2nd item.

33 jump              Unconditional jump.
   dest-$

34 stk-data          Stacks the embedded compressed literal.
   nn                (nn AND &3F)+&50=exponent, (nn DIV &40)+1=number of mantissa bytes
   mm....            mantissa bytes

35 dec-jr-nz         Decrement BREG and branch if non-zero.
   dest-$

36 less-0            Replace top item with 1 if less than zero, otherwise replace with zero.

37 greater-0         Replace top item with 1 if greater than zero, otherwise replace with zero.

38 end-calc          End calculator operations and return to Z80 code.

39 get-argt          Preprocess argument of SIN or COS.

3A truncate          Round integer towards zero. 

3B fp-calc-2         Perform the calculator operation in the B register. This is used to 
                     perform most Basic functions with B=&18 to &30. Replaces top of stack with result.

3C e-to-fp           Calculate constant number xEm (eg 4.5E3). Cannot be called via the calculator as
3C str$hex           A is used to pass a parameter. JGHROM replaces this with STR$~ to convert top item
                     to a hex string.

3D re-stack          Restacks current number in full 5-byte floating form.

Multiple operations
-------------------
8x series-X          Series generator. Calculates the polynomial for X, normally 6, 8 or &C.

Ax stk-const         Stacks a constant.
                      X=0 zero,  X=1 one,  X=2 half,  X=3 PI/2,  X=4 ten.

Cx st-mem-X          Copies top item, storing it in calculator area X.

Ex get-mem-X         Fetches from calculator memory area X, pushes to top of stack.