diff options
Diffstat (limited to 'lib/zip-int-bits.nix')
| -rw-r--r-- | lib/zip-int-bits.nix | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/lib/zip-int-bits.nix b/lib/zip-int-bits.nix new file mode 100644 index 00000000000..edbcdfe1e68 --- /dev/null +++ b/lib/zip-int-bits.nix @@ -0,0 +1,39 @@ +/* Helper function to implement a fallback for the bit operators + `bitAnd`, `bitOr` and `bitXOr` on older nix version. + See ./trivial.nix +*/ +f: x: y: + let + # (intToBits 6) -> [ 0 1 1 ] + intToBits = x: + if x == 0 || x == -1 then + [] + else + let + headbit = if (x / 2) * 2 != x then 1 else 0; # x & 1 + tailbits = if x < 0 then ((x + 1) / 2) - 1 else x / 2; # x >> 1 + in + [headbit] ++ (intToBits tailbits); + + # (bitsToInt [ 0 1 1 ] 0) -> 6 + # (bitsToInt [ 0 1 0 ] 1) -> -6 + bitsToInt = l: signum: + if l == [] then + (if signum == 0 then 0 else -1) + else + (builtins.head l) + (2 * (bitsToInt (builtins.tail l) signum)); + + xsignum = if x < 0 then 1 else 0; + ysignum = if y < 0 then 1 else 0; + zipListsWith' = fst: snd: + if fst==[] && snd==[] then + [] + else if fst==[] then + [(f xsignum (builtins.head snd))] ++ (zipListsWith' [] (builtins.tail snd)) + else if snd==[] then + [(f (builtins.head fst) ysignum )] ++ (zipListsWith' (builtins.tail fst) [] ) + else + [(f (builtins.head fst) (builtins.head snd))] ++ (zipListsWith' (builtins.tail fst) (builtins.tail snd)); + in + assert (builtins.isInt x) && (builtins.isInt y); + bitsToInt (zipListsWith' (intToBits x) (intToBits y)) (f xsignum ysignum) |