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40 lines
1.4 KiB
Nix
40 lines
1.4 KiB
Nix
/* Helper function to implement a fallback for the bit operators
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`bitAnd`, `bitOr` and `bitXor` on older nix version.
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See ./trivial.nix
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*/
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f: x: y:
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let
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# (intToBits 6) -> [ 0 1 1 ]
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intToBits = x:
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if x == 0 || x == -1 then
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[]
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else
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let
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headbit = if (x / 2) * 2 != x then 1 else 0; # x & 1
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tailbits = if x < 0 then ((x + 1) / 2) - 1 else x / 2; # x >> 1
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in
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[headbit] ++ (intToBits tailbits);
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# (bitsToInt [ 0 1 1 ] 0) -> 6
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# (bitsToInt [ 0 1 0 ] 1) -> -6
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bitsToInt = l: signum:
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if l == [] then
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(if signum == 0 then 0 else -1)
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else
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(builtins.head l) + (2 * (bitsToInt (builtins.tail l) signum));
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xsignum = if x < 0 then 1 else 0;
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ysignum = if y < 0 then 1 else 0;
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zipListsWith' = fst: snd:
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if fst==[] && snd==[] then
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[]
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else if fst==[] then
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[(f xsignum (builtins.head snd))] ++ (zipListsWith' [] (builtins.tail snd))
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else if snd==[] then
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[(f (builtins.head fst) ysignum )] ++ (zipListsWith' (builtins.tail fst) [] )
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else
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[(f (builtins.head fst) (builtins.head snd))] ++ (zipListsWith' (builtins.tail fst) (builtins.tail snd));
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in
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assert (builtins.isInt x) && (builtins.isInt y);
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bitsToInt (zipListsWith' (intToBits x) (intToBits y)) (f xsignum ysignum)
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