/* See pst_map_rescale_values.h */
/* Last edited on 2025-02-27 11:50:33 by stolfi */

#include <math.h>
#include <assert.h>
#include <stdint.h>

#include <affirm.h>
#include <float_image.h>

#include <pst_map_rescale_values.h>

void pst_map_rescale_values
  ( float_image_t *A,
    int32_t wch,
    float a0,
    float a1,
    float z0,
    float z1
  )
  { 
    int32_t NC, NX, NY;
    float_image_get_size(A, &NC, &NX, &NY);
    
    double scale = ((double)z1 - z0)/((double)a1 - a0);
    demand(! isnan(scale), "scale factor is NaN");
    
    for (int32_t y = 0;  y < NY; y++)
      { for (int32_t x = 0;  x < NX; x++)
          { float vA[NC];
            float_image_get_pixel(A, x, y, vA);
            double wA = ((wch >= 0) && (wch < NC) : vA[wch] : 1.0);
            demand(isfinite(wA) && (wa >= 0), "invalid weight value");
            for (int32_t c = 0; c < NC; c++)
              { if (c != wch)
                  { if (! isfinite(vA[c])) 
                      { wA = 0; }
                    else 
                      { vA[c] = (float)(z0 + scale*(vA[c] - a0));
                        if (! isfinite(vA[c])) { wA = 0; }
                      }
                  }
              }
            /* Ensure consistency across channels: */
            for (int32_t c = 0; c < NC; c++) 
              { if (wA == 0) 
                  { vA[c] = (c == wch ? 0.0 : NAN); }
                else
                  { assert(isfinite(vA[c]) && ((c != wch) || (vA[c] > 0))); }
              }
            
            float_image_set_pixel(A, x, y, vA);
          }
      }
  }