fix(xlaqp2rk): do not modify [in] argument KMAX; introduce KBOUND#1202
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nakatamaho wants to merge 1 commit intoReference-LAPACK:masterfrom
Open
fix(xlaqp2rk): do not modify [in] argument KMAX; introduce KBOUND#1202nakatamaho wants to merge 1 commit intoReference-LAPACK:masterfrom
nakatamaho wants to merge 1 commit intoReference-LAPACK:masterfrom
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In all four variants (SLAQP2RK, DLAQP2RK, CLAQP2RK, ZLAQP2RK),
KMAX was declared as [in] in the documentation but was overwritten
internally via:
KMAX = MIN( KMAX, MINMNFACT )
This is a bug in the reference LAPACK implementation: the Fortran
calling convention silently tolerates this when the caller passes
a temporary expression, but the intent annotation is violated and
C/C++ translations fail to compile (cannot bind rvalue to non-const
reference).
Introduce local variable KBOUND to hold the clamped value:
KBOUND = MIN( KMAX, MINMNFACT )
and replace all subsequent uses of KMAX in the executable section
(loop bound and final assignment K = KBOUND) with KBOUND.
KMAX itself is no longer modified.
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Summary
In
SLAQP2RK,DLAQP2RK,CLAQP2RK, andZLAQP2RK, the argumentKMAXis documented as[in], but the implementation overwrites it:This is a contradiction between the documentation and the implementation.
Root cause
Fortran callers are insulated from this side effect because
DGEQP3RK(and its variants) pass a temporary expressionJMAX - J + 1rather than a named variable, so the write toKMAXinsidexLAQP2RKis silently discarded. However:[in]annotation is violated.Fix
Introduce a local variable
KBOUNDto hold the clamped value.KMAXis no longer written to.Files changed
SRC/slaqp2rk.fSRC/dlaqp2rk.fSRC/claqp2rk.fSRC/zlaqp2rk.fNo behavior change
The computed result is identical for all existing callers. This is a correctness fix for the argument intent annotation and a robustness fix for non-Fortran consumers of these routines.