dupper.F

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C **********************************************************************

      FUNCTION dupper(V1)
      
      IMPLICIT NONE
      
C...Upper limit on second variable (y, Q**2 or W**2) depending on first
C...variable x=V1. Used for integrating differential cross-section.

*
* to avoid variable conflictions, a second keep element is necessary
* with the same common block name (see LPTOU2)
*
      COMMON /leptou/ cut(14),lst(40),parl(30),
     &                x,y,w2,q2,u
      REAL cut,parl,x,y,w2,q2,u
      INTEGER lst
      SAVE /leptou/

      COMMON /lintrl/ psave(3,4,5),ksave(4),xmin,xmax,ymin,ymax,
     &q2min,q2max,w2min,w2max,ilep,inu,ig,iz
      REAL psave,xmin,xmax,ymin,ymax,q2min,q2max,w2min,w2max
      INTEGER ksave,ilep,inu,ig,iz
      SAVE /lintrl/

      REAL dupper,v1,s,pm2
      
C...CMS energy squared and target nucleon mass.
      s=parl(21)
      pm2=psave(3,2,5)**2
      IF(lst(31).EQ.1) THEN
        dupper=min(q2max,v1*ymax*s,(w2max-pm2)*v1/max(1.-v1,1.e-22))
      ELSEIF(lst(31).EQ.2) THEN
        dupper=min(ymax,q2max/(s*v1),(w2max-pm2)/max(s*(1.-v1),1.e-22))
      ELSEIF(lst(31).EQ.3) THEN
        dupper=min(w2max,(1.-v1)*ymax*s+pm2,
     &  q2max*(1.-v1)/max(v1,1.e-22)+pm2)
      ENDIF
      RETURN
      END