%lagoon sub-rays jet don't work right

[yapishu]

the %sub-rays jet from the lagoon lib subtracts out of order, ie (sub a b) evaluates as (sub b a). Here's the relevant PR in numerics by @sigilante : urbit/numerics#20

the c jet calls saxpy(N, -1, x_bytes, 1, y_bytes, 1). axpy semantics are Y := alpha*X + Y, so with alpha=-1 you get Y = y - x, then it returns y_bytes. but the hoon contract (sub:la a b) is supposed to give a - b, and the jet loaded a as x_data and b as y_data, so it returns b - a. this wasn't picked up by tests because the only test case was subtracting two ones

urbit -F zod
> |new-desk %lagoon
> |mount %lagoon
git clone https://github.com/urbit/numerics
mkdir -p zod/lagoon
cp -Lr numerics/lagoon/desk/* zod/lagoon/
echo '[%zuse 409]' > zod/lagoon/sys.kelvin

edit zod/lagoon/lib/lagoon.hoon, find ++ sub (~line 903), add a copy right after it called sub2 with no jet hint:

++  sub   :: original, jetted
  ~/  %sub-rays
  |=  [a=ray b=ray]
  ^-  ray
  (bin-op a b (fun-scalar meta.a %sub))
++  sub2  :: identical body, no jet
  |=  [a=ray b=ray]
  ^-  ray
  (bin-op a b (fun-scalar meta.a %sub))

drop this in zod/lagoon/gen/test-sub.hoon:

/-  ls=lagoon
/+  *lagoon
:-  %say
|=  *
:-  %noun
=/  la  (lake %n)
=/  meta=meta:ls  [~[1] 5 %i754 ~]
=/  a-ray  (fill:la meta .5)
=/  b-ray  (fill:la meta .2)
=/  diff  (sub:la a-ray b-ray)
=/  v  `@rs`(get-item:la diff ~[0])
~&  >  ['(sub:la 5.0 2.0)' v]
~&  >  ['Jetted' ~]
~&  >  ?:(=(v .3) 'PASS — a - b' ?:(=(v .-3) 'FAIL — b - a' 'FAIL — other'))
~&  >  ['Unjetted' ~]
=/  diff2  (sub2:la a-ray b-ray)
=/  v  `@rs`(get-item:la diff2 ~[0])
~&  >  ['(sub2:la 5.0 2.0)' v]
~&  >  ?:(=(v .3) 'PASS — a - b' ?:(=(v .-3) 'FAIL — b - a' 'FAIL — other'))
~

> |commit %lagoon
> +lagoon!test-sub

Output:

>   ['(sub:la 5.0 2.0)' .-3]
>   ['Jetted' ~]
>   'FAIL — b - a'
>   ['Unjetted' ~]
>   ['(sub2:la 5.0 2.0)' .3]
>   'PASS — a - b'

[mopfel-winrux]

urbit/numerics#20 should fix it, we will get it in