form_rot.h

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/* Copyright (C) 2026 Chris Piker <chris-piker@uiowa.edu>
 *
 * Author: C. Piker, via Claude Opus 5
 *
 * This file is part of das2C, the Core Das2 C Library.
 *
 * Das2C is free software; you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License version 2.1 as published
 * by the Free Software Foundation.
 *
 * Das2C is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
 * more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * version 2.1 along with das2C; if not, see <http://www.gnu.org/licenses/>.
 */
 
#ifndef _das_form_rot_h_
#define _das_form_rot_h_
 
#include <das3/form.h>
 
#ifdef __cplusplus
extern "C" {
#endif
 
/* Exported so that its address can be compared.  One object in the whole
   program, so its address answers "is this partner a rotation?".  Client code
   uses the DAS_FORM_ROT macro below and has no reason to name this directly. */
DAS_API extern const DasForm_VTbl das_form_rotate_vtbl;
 
#define DAS_FORM_ROT (&das_form_rotate_vtbl)
 
 
/* The two representations, as element counts.  A rotation's shape is NOT
   stored on the form: it is the operand's declared intern=, and it arrives in
   a das_operand.  Storing it in both places is how the two drift apart.
 
   Canonical element order, which is what sysorder= indexes:
 
     matrix      0 xx  1 xy  2 xz  3 yx  4 yy  5 yz  6 zx  7 zy  8 zz
                 row major, row is the to= axis and column the from= axis
     quaternion  0 w   1 x   2 y   3 z
                 scalar first, SPICE's convention
 
   A stream storing a matrix column major says sysorder="0;3;6;1;4;7;2;5;8";
   one storing a quaternion scalar last says sysorder="1;2;3;0".  Every element
   must be placed: a rotation has no default for a missing one. */
#define ROT_MATRIX  9    /* intern="3;3" */
#define ROT_QUAT    4    /* intern="4" */
 
DAS_API int DasFormRotate_layout(const das_operand* pOp);
 
 
DAS_API DasForm* new_DasFormRotate(const char* sFrom, const char* sTo);
 
DAS_API const char* DasFormRotate_from(const DasForm* pThis);
 
DAS_API const char* DasFormRotate_to(const DasForm* pThis);
 
#ifdef __cplusplus
}
#endif
 
#endif /* _das_form_rot_h_ */