generalized 16-bit fixed-width math
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( fix16.tal )
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( )
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( use a signed 16-bit short as a fixed point number. )
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( )
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( numbers are interpreted as fractions with an implicit )
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( 256 denominator. the upper byte is signed and )
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( represents the "whole" part of the number, and the )
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( lower byte is unsigned and represents the )
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( "fractional" part of the number. )
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( )
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( 16-bit fixed point can represent fractional values )
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( in the range -128 <= x < 128. the smallest fraction it )
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( can represent is 1/256, which is about 0.004. )
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( )
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( SHORT FRACTION DECIMAL )
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( #0000 0/256 0.000 )
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( #0001 1/256 0.004 )
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( #0002 2/256 0.008 )
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( #0040 64/256 0.250 )
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( #0080 128/256 0.500 )
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( #0100 256/256 1.000 )
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( #0700 1792/256 7.000 )
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( #7f00 32512/256 127.000 )
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( #7fff 32767/256 127.996 )
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( #8000 -32768/256 -128.000 )
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( #8001 -32767/256 -127.996 )
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( #8100 -32767/256 -127.000 )
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( #ff00 -256/256 -1.000 )
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( #ffff -1/256 -0.004 )
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( )
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( many 8.8 operations are equivalent to u16: )
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( * comparisons/equality )
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( * addition/subtraction )
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( * division )
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( )
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( but due to 16-bit truncation multiplication differs... )
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( )
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( x*y = x0*y0 + x0*y1/256 + x1*y0/256 + x1*y1/65536 )
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( )
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( since we only have 16-bits: )
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( 1. we need to drop the 8 high bits from x0*y0 )
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( 2. we need to drop the 8 low bits from x1*y1 )
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( 3. we need to use all the bits from x0*y1 and x1*y0 )
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( )
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( that said, if either x or y is whole (i.e. ends in 00) )
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( then we can just shift that argument right by 8 and use )
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( MUL2 as normal. )
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|1000
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( useful constants )
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( )
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( to generate your own: )
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( 1. take true value, e.g. 3.14159... )
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( 2. multiply by 256 )
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( 3. round to nearest whole number )
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( 4. emit hex output )
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( )
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( in python: hex(round(x * 256)) )
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%x16-zero { #0000 } ( 0.0 )
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%x16-one { #0100 } ( 1.0 )
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%x16-two { #0200 } ( 2.0 )
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%x16-ten { #0a00 } ( 10.0 )
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%x16-hundred { #6400 } ( 100.0 )
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%x16-minus-one { #7f00 } ( -1.0 )
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%x16-minus-two { #7e00 } ( -2.0 )
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%x16-pi/2 { #0192 } ( 1.57079... )
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%x16-pi { #0324 } ( 3.14159... )
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%x16-pi*2 { #0648 } ( 6.28318... )
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%x16-e { #02b8 } ( 2.71828... )
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%x16-phi { #019e } ( 1.61803... )
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%x16-sqrt-2 { #016a } ( 1.41421... )
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%x16-sqrt-3 { #01bb } ( 1.73205... )
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%x16-epsilon { #0001 } ( 0.00390625 )
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%x16-minimum { #8000 } ( -128.0 )
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%x16-maximum { #7fff } ( 127.99609375 )
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( useful macros )
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%x16-is-non-neg { x16-minimum LTH2 }
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%x16-is-neg { x16-maximum GTH2 }
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( comparison between x and y. )
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( - ff: x < y )
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( - 00: x = y )
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( - 01: x > y )
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@x16-cmp ( x* y* -> c^ )
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STH2k x16-is-neg ,&yn JMP
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x16-is-non-neg ,&ypxp ( y>=0 )
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POP2 POP2r #ff JMP2r ( x<0 y>=0 )
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&ypxp ;x16-ucmp JMP2 ( x>=0 y>=0 )
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&yn x16-is-neg ,&ynxn ( y<0 )
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POP2 POP2r #01 JMP2r ( x>=0 y<0 )
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&ynxn SWP2 ;x16-ucmp JMP2 ( x<0 y<0 )
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( unsigned comparison between x and y. )
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( - ff: x < y )
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( - 00: x = y )
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( - 01: x > y )
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@x16-ucmp ( x* y* -> c^ )
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LTH2k ,< JCN GTH2 JMP2r
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< POP2 POP2 #ff JMP2r
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@x16-eq ( x* y* -> x=y ) EQU2 JMP2r
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@x16-ne ( x* y* -> x!=0 ) NEQ2 JMP2r
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@x16-lt ( x* y* -> x<y^ ) ;x16-cmp JSR2 #ff EQU JMP2r
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@x16-lteq ( x* y* -> x<y^ ) ;x16-cmp JSR2 #01 NEQ JMP2r
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@x16-gt ( x* y* -> x<y^ ) ;x16-cmp JSR2 #01 EQU JMP2r
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@x16-gteq ( x* y* -> x<y^ ) ;x16-cmp JSR2 #ff NEQ JMP2r
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@x16-is-whole ( x* -> bool^ )
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NIP #00 EQU JMP2r
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@x16-add ( x* y* -> x+y* )
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ADD2 JMP2r
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@x16-sub ( x* y* -> x-y* )
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SUB2 JMP2r
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@x16-negate ( x* -> -x* )
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#0000 SWP2 SUB2 JMP2r
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@x16-mul ( x* y* -> xy* )
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DUP #00 EQU ,&rhs-whole JCN
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SWP2 DUP #00 EQU ,&rhs-whole JCN
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,&y3 STR ,&y1 STR ,&x3 STR ,&x1 STR
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LIT2 &x2 00 &x3 00 LIT2 &y2 00 &y3 00 MUL2 #08 SFT2
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LIT2 &x0 00 &x1 00 ,&y2 LDR2 MUL2 ADD2
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,&x2 LDR2 LIT2 &y0 00 &y1 00 MUL2 ADD2
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,&x0 LDR2 ,&x0 LDR2 MUL2 #80 SFT2 ADD2 JMP2r
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&rhs-whole #08 SFT2 MUL2 JMP2r
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@x16-div ( x* y* -> x/y* )
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SWP2 DUP2 x16-is-non-neg ,&non-negative ( y x )
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;x16-negate JSR2 SWP2 DIV2 ;x16-negate JMP2
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&non-negative
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SWP2 DIV2 JMP2r
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@x16-mod ( x* y* -> x%y* )
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;x16-div JSR2 ;x16-mul JSR2 SUB2 JMP2r
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@x16-mod-div ( x* y* -> x%y* x/y* )
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;x16-div JSR2 STH2k ;x16-mul JSR2 SUB2 STH2r JMP2r
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@x16-div-mod ( x* y* -> x/y* x%y* )
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;x16-mod-div JSR2 SWP2 JMP2r
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