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fix(thinc): restore ln2/f_log_cosh to keep AMD omptarget module-data layout #1416

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fix(thinc): restore ln2/f_log_cosh to keep AMD omptarget module-data layout #1416

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7be7cf0
fix(thinc): use create= for GPU_DECLARE of static-init quadrature arrays
sbryngelson May 10, 2026
b6a7f4c
fix(thinc): restore ln2 + f_log_cosh to keep AMD omptarget module-dat…
sbryngelson May 10, 2026
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20 changes: 19 additions & 1 deletion src/simulation/m_thinc.fpp
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Expand Up @@ -30,14 +30,32 @@ module m_thinc
real(wp) :: gq3_pts(3) = [-5e-1_wp*0.7745966692414834_wp, 0._wp, 5e-1_wp*0.7745966692414834_wp]
!> Weights: 5/18, 8/18, 5/18
real(wp) :: gq3_wts(3) = [5._wp/18._wp, 8._wp/18._wp, 5._wp/18._wp]
$:GPU_DECLARE(copyin='[gq3_pts, gq3_wts]')
!> ln(2)
real(wp) :: ln2 = 0.6931471805599453_wp
$:GPU_DECLARE(create='[gq3_pts, gq3_wts, ln2]')

real(wp), allocatable, dimension(:,:,:,:) :: mthinc_nhat !> Unit normal vector
real(wp), allocatable, dimension(:,:,:) :: mthinc_d !> Interface position parameter
$:GPU_DECLARE(create='[mthinc_nhat, mthinc_d]')

contains

!> @brief Stable computation of ln(cosh(x))
function f_log_cosh(x) result(res)

$:GPU_ROUTINE(parallelism='[seq]')
real(wp), intent(in) :: x
real(wp) :: res, ax

ax = abs(x)
if (ax > 20._wp) then
res = ax - ln2
else
res = ax + log(1._wp + exp(-2._wp*ax)) - ln2
end if

end function f_log_cosh

!> @brief Stable difference: log_cosh(a+h) - log_cosh(a-h) = 2*atanh(tanh(a)*tanh(h)). Avoids catastrophic cancellation when h
!! is small relative to a.
function f_log_cosh_diff(a, h) result(res)
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