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lib/trivial: move zipIntBits to its own file
The amount of implementation detail really should not be the first thing in a prominent file called `trivial.nix`.
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@ -1,41 +1,5 @@
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{ lib }:
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let
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zipIntBits = 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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in
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rec {
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## Simple (higher order) functions
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@ -71,13 +35,19 @@ rec {
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and = x: y: x && y;
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/* bitwise “and” */
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bitAnd = builtins.bitAnd or zipIntBits (a: b: if a==1 && b==1 then 1 else 0);
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bitAnd = builtins.bitAnd
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or import ./zip-int-bits.nix
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(a: b: if a==1 && b==1 then 1 else 0);
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/* bitwise “or” */
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bitOr = builtins.bitOr or zipIntBits (a: b: if a==1 || b==1 then 1 else 0);
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bitOr = builtins.bitOr
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or import ./zip-int-bits.nix
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(a: b: if a==1 || b==1 then 1 else 0);
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/* bitwise “xor” */
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bitXor = builtins.bitXor or zipIntBits (a: b: if a!=b then 1 else 0);
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bitXor = builtins.bitXor
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or import ./zip-int-bits.nix
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(a: b: if a!=b then 1 else 0);
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/* bitwise “not” */
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bitNot = builtins.sub (-1);
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39
lib/zip-int-bits.nix
Normal file
39
lib/zip-int-bits.nix
Normal file
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@ -0,0 +1,39 @@
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/* 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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