Restore mac tests but on ARM

[dlfivefifty]

This is to see if Mac tests pass on ARM (before we were testing on x64)

also bumps setup-julia

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.47%. Comparing base (14a3118) to head (84139eb).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #268      +/-   ##
==========================================
+ Coverage   74.75%   77.47%   +2.72%     
==========================================
  Files          17       17              
  Lines        3208     3228      +20     
==========================================
+ Hits         2398     2501     +103     
+ Misses        810      727      -83     

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[dlfivefifty]

no dice

[dlfivefifty]

@copilot why are tests failing?

[Copilot]

@copilot why are tests failing?

The tests are failing due to the same issue as #263 — a segfault (signal 11) in the libfasttransforms tests on Julia 1.12, but passing fine on Julia LTS.

What's failing:

• Julia 1 - ubuntu-latest: ❌ signal 11 in libfasttransformstests.jl:5
• Julia 1 - macOS-latest (ARM): ❌ signal 11 in libfasttransformstests.jl:5
• Julia lts - ubuntu-latest: ✅ passes
• Julia lts - macOS-latest (ARM): ✅ passes

Root cause (stack trace on macOS ARM):

__gmpn_mul_basecase → mpfr_mul → ft_mpfr_trmv_ptr → lmul! (libfasttransforms.jl:986) → * (libfasttransforms.jl:880) → test_1d_plans (libfasttransformstests.jl:28)

The crash occurs in ft_mpfr_trmv_ptr when the C library performs MPFR arithmetic on the input BigFloat vector. The BigFloat struct layout changed in Julia 1.12 (likely related to the allocation-free BigFloat changes), so when the C function reads the Julia BigFloat array elements as mpfr_t*, it reads corrupted/incompatible memory, causing GMP to segfault.

This is a Julia 1.12 compatibility issue with the BigFloat path in the C library — so the Mac ARM runner confirms the same behavior as Linux. The fix needs to address how Ptr{BigFloat} is passed to ft_mpfr_trmv_ptr / ft_mpfr_trsv_ptr (and the matrix variants) in src/libfasttransforms.jl, likely by updating the mpfr_t struct definition or the renew! function to match Julia 1.12's new BigFloat layout.

[dlfivefifty]

@copilot can you make a PR to fix this?

[Copilot]

@copilot can you make a PR to fix this?

Done. The fix is in commit Fix BigFloat Julia 1.12 compatibility.

Root cause: In Julia 1.12, BigFloat changed from a mutable struct whose fields matched mpfr_t directly to an immutable struct wrapping Memory{Limb}. The ft_mpfr_trmv_ptr/trsv/trmm/trsm C functions expect mpfr_t** (array of pointers to mpfr_t structs), but the old Ptr{BigFloat} was now passing pointers to BigFloat wrapper objects rather than to the actual mpfr_t structs.

Fix: Added _mpfr_ptr(b::BigFloat) (version-dispatched) to extract the correct mpfr_t*:

• Julia ≥ 1.12: pointer(getfield(b, :d)) — the Memory{Limb} stores the mpfr_t struct at its start
• Julia < 1.12: pointer_from_objref(b) — the mutable BigFloat's fields are layout-compatible with mpfr_t

All 42 BigFloat 1D plan tests now pass on Julia 1.12.

[dlfivefifty]

@MikaelSlevinsky can I approve this to run?