bytes->i64 is strtoll behind a primitive, and strtoll returns 0 for "", for
"abc", for a lone "-", and for the "12" in "12x". None of those is
distinguishable from a real 0, so any program that parses input it did not
write is already wrong and has no way to find out. parse-i64 takes the whole
slice or refuses it and says so with None. It is also the version that answers
the same on wasm32: strtoll is libc's and locale-sensitive, which is the same
argument that put the PRNG in the prelude rather than leaving it to rand().
The byte predicates are over [u8] rather than over string on purpose. (bytes s)
is one call at the call site, and in exchange one copy of each function serves
strings and byte slices both — which is as near a generic as this gets. Each
tests its length before it slices, and `and` short-circuits, so a prefix longer
than the subject answers false instead of tripping the slice bounds check.
sign-f32 and lerp are the only two numeric helpers here, because they are the
only two that decide something. clamp is (min hi (max lo x)) and abs is
(max x (- 0 x)) over builtins that already exist — a prelude wrapper is a
function emitted into every program to save a caller nothing. sign-f32 answers
0.0 for NaN, which is a choice and is written down. lerp is the weighted sum
and not a + t*(b - a): the latter does not land on b exactly at t = 1.0, and a
position that never quite arrives is what interpolation gets bug reports for.
floor, ceil and round are deliberately absent. (f32 (i32 x)) is fptosi, which
is poison out of range, and shipping that as a documented limitation is the
same class of bug NEXT.md already records twice under Sharp edges. Correct
lowering is llvm.floor.f32 in emit.ml, which is not this lane. sqrt is absent
for a different reason: it is an extern to libm, and what libm means on wasm32
is a decision the FFI owns, not the prelude.
rand-i32-range answers lo for an empty or reversed range rather than dividing
by zero, which is immediate undefined behaviour and not merely a wrong number.
Both range functions draw exactly one rand-u32 and neither changes it, so the
sand hash still pins the generator; the new test pins the derivations off a
fixed seed, which nothing else would have caught.
Joseph Ferano
7fcda905ff