#include "isajet/pilot.h"
      SUBROUTINE SIGGAM
C
C          Compute D(SIGMA)/D(PT**2)D(Y1)D(Y2) for gamma + jet and
C          gamma + gamma.
C
C          SIGMA    = cross section summed over quark types allowed by
C                     JETTYPE card.
C          SIGS(I)  = partial cross section for I1 + I2 --> I3 + I4.
C          INOUT(I) = IOPAK**3*I4 + IOPAK**2*I3 + IOPAK*I2 + I1
C                     using JETTYPE code.
C
C          Cross sections from Berger, Bratten, and Field, Nucl. Phys.
C          B239, 52 (1984), Table 2. Masses are neglected.
C
C
#if defined(CERNLIB_IMPNONE)
      IMPLICIT NONE
#endif
#include "isajet/itapes.inc"
#include "isajet/qcdpar.inc"
#include "isajet/jetpar.inc"
#include "isajet/primar.inc"
#include "isajet/q1q2.inc"
#include "isajet/jetsig.inc"
#include "isajet/const.inc"
#include "isajet/wcon.inc"
C
      REAL BBF1,BBF2,BBF3,S,T,U,FJAC,STRUC,SIG0,SIG,BBF3TU,BBF3UT
      INTEGER I,IH,IQ,IFL
      REAL X(2),QSAVE(13,2)
      INTEGER LISTJ(13)
      EQUIVALENCE (X(1),X1),(S,SHAT),(T,THAT),(U,UHAT)
      DATA LISTJ/9,1,-1,2,-2,3,-3,4,-4,5,-5,6,-6/
C
C          Cross sections with couplings and Jacobean removed.
      BBF1(S,T,U)=8./9.*(U/T+T/U)
      BBF2(S,T,U)=2./3.*(U/T+T/U)
      BBF3(S,T,U)=-1./3.*(U/S+S/U)
C
C          Initialize cross sections.
C
      SIGMA=0.
      NSIGS=0
      DO 100 I=1,MXSIGS
      SIGS(I)=0.
100   CONTINUE
C
C          Kinematics and structure functions for CH and lighter quarks
C
      CALL TWOKIN(0.,0.,0.,0.)
      FJAC=SHAT/SCM*UNITS*PI/SHAT**2
      IF(X1.GE.1.0.OR.X2.GE.1.0) RETURN
      DO 110 IH=1,2
      DO 110 IQ=1,9
        QSAVE(IQ,IH)=STRUC(X(IH),QSQ,IQ,IDIN(IH))/X(IH)
110   CONTINUE
C
C          Compute cross sections summed over all types allowed by
C          JETTYPE card.
C
      IF(.NOT.(GOQ(26,1).OR.GOQ(26,2))) RETURN
C
C          Gluon-photon
C
      IF((GOQ(1,1).AND.GOQ(26,2)).OR.(GOQ(26,1).AND.GOQ(1,2))) THEN
        SIG0=.5*FJAC*ALFQSQ*ALFA*BBF1(S,T,U)
        DO 210 I=1,4
          IFL=LISTJ(2*I)
          SIG=SIG0*AQ(IFL,1)**2*QSAVE(2*I,1)*QSAVE(2*I+1,2)
          IF(GOQ(26,1).AND.GOQ(1,2)) CALL SIGFIL(SIG,2*I,2*I+1,26,1)
          IF(GOQ(1,1).AND.GOQ(26,2)) CALL SIGFIL(SIG,2*I,2*I+1,1,26)
          SIG=SIG0*AQ(IFL,1)**2*QSAVE(2*I+1,1)*QSAVE(2*I,2)
          IF(GOQ(26,1).AND.GOQ(1,2)) CALL SIGFIL(SIG,2*I+1,2*I,26,1)
          IF(GOQ(1,1).AND.GOQ(26,2)) CALL SIGFIL(SIG,2*I+1,2*I,1,26)
210     CONTINUE
      ENDIF
C
C          Photon-photon
C
      IF(GOQ(26,1).AND.GOQ(26,2)) THEN
        SIG0=.5*FJAC*ALFA**2*BBF2(S,T,U)
        DO 220 I=1,4
          IFL=LISTJ(2*I)
          SIG=SIG0*AQ(IFL,1)**4*QSAVE(2*I,1)*QSAVE(2*I+1,2)
          CALL SIGFIL(SIG,2*I,2*I+1,26,26)
          SIG=SIG0*AQ(IFL,1)**4*QSAVE(2*I+1,1)*QSAVE(2*I,2)
          CALL SIGFIL(SIG,2*I+1,2*I,26,26)
220     CONTINUE
      ENDIF
C
C          Quark-photon
C
      BBF3TU=.5*FJAC*ALFA*ALFQSQ*BBF3(S,T,U)
      BBF3UT=.5*FJAC*ALFA*ALFQSQ*BBF3(S,U,T)
      DO 230 I=2,9
        IFL=IABS(LISTJ(I))
        IF(GOQ(26,1).AND.GOQ(I,2)) THEN
          SIG=BBF3TU*AQ(IFL,1)**2*QSAVE(I,1)*QSAVE(1,2)
          CALL SIGFIL(SIG,I,1,26,I)
          SIG=BBF3UT*AQ(IFL,1)**2*QSAVE(1,1)*QSAVE(I,2)
          CALL SIGFIL(SIG,1,I,26,I)
        ENDIF
        IF(GOQ(I,1).AND.GOQ(26,2)) THEN
          SIG=BBF3UT*AQ(IFL,1)**2*QSAVE(I,1)*QSAVE(1,2)
          CALL SIGFIL(SIG,I,1,I,26)
          SIG=BBF3TU*AQ(IFL,1)**2*QSAVE(1,1)*QSAVE(I,2)
          CALL SIGFIL(SIG,1,I,I,26)
        ENDIF
230   CONTINUE
C
      RETURN
      END