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Prevent compilers from using FMA instructions #1033

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Merged
merged 2 commits into from
Jul 13, 2024
Merged

Prevent compilers from using FMA instructions #1033

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22f9be6
Added parentheses to multiplications to prevent compilers from using …
ACSimon33 Jul 12, 2024
349b76a
Remove trailing whitespace
ACSimon33 Jul 12, 2024
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10 changes: 7 additions & 3 deletions SRC/dlanv2.f
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Original file line number Diff line number Diff line change
Expand Up @@ -144,7 +144,7 @@ SUBROUTINE DLANV2( A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS, SN )
* ..
* .. Local Scalars ..
DOUBLE PRECISION AA, BB, BCMAX, BCMIS, CC, CS1, DD, EPS, P, SAB,
$ SAC, SCALE, SIGMA, SN1, TAU, TEMP, Z, SAFMIN,
$ SAC, SCALE, SIGMA, SN1, TAU, TEMP, Z, SAFMIN,
$ SAFMN2, SAFMX2
INTEGER COUNT
* ..
Expand Down Expand Up @@ -248,10 +248,14 @@ SUBROUTINE DLANV2( A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS, SN )
*
* Compute [ A B ] = [ CS SN ] [ AA BB ]
* [ C D ] [-SN CS ] [ CC DD ]
*
* Note: Some of the multiplications are wrapped in parentheses to
* prevent compilers from using FMA instructions. See
* https://github.com/Reference-LAPACK/lapack/issues/1031.
*
A = AA*CS + CC*SN
B = BB*CS + DD*SN
C = -AA*SN + CC*CS
B = ( BB*CS ) + ( DD*SN )
C = -( AA*SN ) + ( CC*CS )
D = -BB*SN + DD*CS
*
TEMP = HALF*( A+D )
Expand Down
10 changes: 7 additions & 3 deletions SRC/slanv2.f
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Expand Up @@ -144,7 +144,7 @@ SUBROUTINE SLANV2( A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS, SN )
* ..
* .. Local Scalars ..
REAL AA, BB, BCMAX, BCMIS, CC, CS1, DD, EPS, P, SAB,
$ SAC, SCALE, SIGMA, SN1, TAU, TEMP, Z, SAFMIN,
$ SAC, SCALE, SIGMA, SN1, TAU, TEMP, Z, SAFMIN,
$ SAFMN2, SAFMX2
INTEGER COUNT
* ..
Expand Down Expand Up @@ -248,10 +248,14 @@ SUBROUTINE SLANV2( A, B, C, D, RT1R, RT1I, RT2R, RT2I, CS, SN )
*
* Compute [ A B ] = [ CS SN ] [ AA BB ]
* [ C D ] [-SN CS ] [ CC DD ]
*
* Note: Some of the multiplications are wrapped in parentheses to
* prevent compilers from using FMA instructions. See
* https://github.com/Reference-LAPACK/lapack/issues/1031.
*
A = AA*CS + CC*SN
B = BB*CS + DD*SN
C = -AA*SN + CC*CS
B = ( BB*CS ) + ( DD*SN )
C = -( AA*SN ) + ( CC*CS )
D = -BB*SN + DD*CS
*
TEMP = HALF*( A+D )
Expand Down