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Don't zero out destination in generic_matvecmul #1242

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Don't zero out destination in generic_matvecmul #1242

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7703ae2
Don't zero out destination in generic_matvecmul
jishnub Mar 17, 2025
6513bf5
Merge branch 'master' into jishnub/genmatvecmul_onepass
jishnub Apr 1, 2025
6c4440d
Merge branch 'master' into jishnub/genmatvecmul_onepass
ViralBShah May 8, 2025
90249c1
Merge branch 'master' into jishnub/genmatvecmul_onepass
ViralBShah Jun 2, 2025
5adb406
Merge branch 'master' into jishnub/genmatvecmul_onepass
dkarrasch Aug 21, 2025
04041c4
fix type promotion
dkarrasch Aug 21, 2025
aff37ab
spell out the muladdmul
dkarrasch Aug 21, 2025
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16 changes: 7 additions & 9 deletions src/matmul.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -951,20 +951,18 @@ function __generic_matvecmul!(::typeof(identity), C::AbstractVector, A::Abstract
alpha::Number, beta::Number)
Astride = size(A, 1)
@inbounds begin
for i = eachindex(C)
if !iszero(beta)
C[i] *= beta
elseif length(B) == 0
for i in eachindex(C)
if length(B) == 0
C[i] = false
else
C[i] = zero(A[i]*B[1] + A[i]*B[1])
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I don't really see how to get this working, without modifying the corresponding test case, which fails for all commits on this branch. We need this sum here to be able to promote to the eltype of C, but we don't have zero available for neither A nor B. If this doesn't affect performance too much, maybe it's not worth it after all?

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Yes, probably not worth it

@stable_muladdmul _modify!(MulAddMul(alpha, beta), A[i]*B[1], C, i)
end
end
for k = eachindex(B)
for k in @view eachindex(B)[2:end]
aoffs = (k-1)*Astride
b = @stable_muladdmul MulAddMul(alpha,false)(B[k])
for i = eachindex(C)
C[i] += A[aoffs + i] * b
bα = @stable_muladdmul MulAddMul(alpha,false)(B[k])
for i in eachindex(C)
C[i] += A[aoffs + i] * bα
end
end
end
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