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Draft: work on eliminating the if condition #17

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Draft: work on eliminating the if condition #17

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1d8c856
ffn: Fuse some of the operations
certik Mar 7, 2023
2399607
Implement faster tanh(x) function
certik Mar 7, 2023
7b4a1f0
Work on eliminating the if condition
certik Mar 8, 2023
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34 changes: 30 additions & 4 deletions gpt2.f90
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Original file line number Diff line number Diff line change
Expand Up @@ -7,9 +7,28 @@ module gpt2_mod

contains

elemental real(sp) function fast_tanh(x) result(y)
real(sp), intent(in) :: x
real(sp) :: x2
x2 = x*x
y = x * (0.98569772605911309407 + x2 *(-0.2794500993392901382 &
+ x2 * (6.8280504526399188164e-2 + x2 * (-1.0972014877337651823e-2 &
+ x2 * (1.1132367134444316902e-3 + x2 * (-7.018851897305717565e-5 &
+ x2 * (2.656616768082727089e-6 + x2 * (-5.5138381821615909058e-8 &
+ x2 * 4.8162484477588665996e-10))))))))
if (x > 5) then
y = 1
! Does not work yet, but would eliminate the if condition
!y = 0.5_sp * (1-sign(1.0, x-5)) * (y-1) + 1
end if
if (x < -5) then
y = -1
end if
end function

elemental real(sp) function gelu(x) result(y)
real(sp), intent(in) :: x
y = 0.5_sp * x * (1 + tanh(sqrt(2 / pi) * (x + 0.044715_sp * x**3)))
y = 0.5_sp * x * (1 + fast_tanh(sqrt(2 / pi) * (x + 0.044715_sp * x**3)))
end function

function softmax(x) result(y)
Expand Down Expand Up @@ -56,9 +75,16 @@ function linear(x, w, b) result(y)
function ffn(x, fc_w, fc_b, proj_w, proj_b) result(y)
real(sp), intent(in) :: x(:,:), fc_w(:,:), fc_b(:), proj_w(:,:), proj_b(:)
real(sp) :: y(size(x,1),size(x,2))
!real(sp) :: a(4*size(x,1),size(x,2))
!a = gelu(linear(x, fc_w, fc_b))
y = linear(gelu(linear(x, fc_w, fc_b)), proj_w, proj_b)
real(sp) :: a(4*size(x,1),size(x,2))
integer :: i, j
!a = linear(x, fc_w, fc_b)
call matmul_2d(fc_w, x, a)
do j = 1, size(a,1)
do i = 1, size(a,2)
a(j,i) = gelu(a(j,i) + fc_b(j))
end do
end do
y = linear(a, proj_w, proj_b)
end function

function attention(q, k, v, mask) result(y)
Expand Down