Use enumerations where appropriate

Enumerations have the following advantages over #define:
- they clearly connect a variable and the allowed constants,
- the meaning of code is not obfuscated by integer values,
- they are visible to the compiler, which can warn about (possibly)
  incorrect usage.

There should be no functional change.

11 files changed, 113 insertions, 76 deletions

diff --git a/src/PJ_aeqd.c b/src/PJ_aeqd.c
index f0c813f5..aa1597e4 100644
--- a/src/PJ_aeqd.c
+++ b/src/PJ_aeqd.c
@@ -31,6 +31,13 @@
 #include <errno.h>
 #include "projects.h"
 
+enum Mode {
+    N_POLE = 0,
+    S_POLE = 1,
+    EQUIT  = 2,
+    OBLIQ  = 3,
+};
+
 struct pj_opaque {
     double  sinph0;
     double  cosph0;
@@ -40,7 +47,7 @@ struct pj_opaque {
     double  Mp;
     double  He;
     double  G;
-    int     mode;
+    enum Mode mode;
     struct geod_geodesic g;
 };
 
@@ -49,11 +56,6 @@ PROJ_HEAD(aeqd, "Azimuthal Equidistant") "\n\tAzi, Sph&Ell\n\tlat_0 guam";
 #define EPS10 1.e-10
 #define TOL 1.e-14
 
-#define N_POLE  0
-#define S_POLE  1
-#define EQUIT   2
-#define OBLIQ   3
-
 
 static void *destructor (PJ *P, int errlev) {                        /* Destructor */
     if (0==P)
diff --git a/src/PJ_airy.c b/src/PJ_airy.c
index a5ee1f24..3b145475 100644
--- a/src/PJ_airy.c
+++ b/src/PJ_airy.c
@@ -34,22 +34,24 @@
 PROJ_HEAD(airy, "Airy") "\n\tMisc Sph, no inv.\n\tno_cut lat_b=";
 
 
+enum Mode {
+    N_POLE = 0,
+    S_POLE = 1,
+    EQUIT  = 2,
+    OBLIQ  = 3,
+};
+
 struct pj_opaque {
     double  p_halfpi;
     double  sinph0;
     double  cosph0;
     double  Cb;
-    int     mode;
+    enum Mode mode;
     int     no_cut; /* do not cut at hemisphere limit */
 };
 
 
 # define EPS 1.e-10
-# define N_POLE 0
-# define S_POLE 1
-# define EQUIT  2
-# define OBLIQ  3
-
 
 
 static XY s_forward (LP lp, PJ *P) {           /* Spheroidal, forward */
diff --git a/src/PJ_aitoff.c b/src/PJ_aitoff.c
index 8e9201d0..4e2f2092 100644
--- a/src/PJ_aitoff.c
+++ b/src/PJ_aitoff.c
@@ -34,9 +34,14 @@
 #include "projects.h"
 
 
+enum Mode {
+    AITOFF = 0,
+    WINKEL_TRIPEL = 1
+};
+
 struct pj_opaque {
     double  cosphi1;
-    int     mode;
+    enum Mode mode;
 };
 
 
@@ -60,7 +65,7 @@ static XY s_forward (LP lp, PJ *P) {           /* Spheroidal, forward */
         xy.y *= d * sin(lp.phi);
     } else
         xy.x = xy.y = 0.;
-    if (Q->mode) { /* Winkel Tripel */
+    if (Q->mode == WINKEL_TRIPEL) {
         xy.x = (xy.x + lp.lam * Q->cosphi1) * 0.5;
         xy.y = (xy.y + lp.phi) * 0.5;
     }
@@ -112,7 +117,7 @@ static LP s_inverse (XY xy, PJ *P) {           /* Spheroidal, inverse */
                 f1l = cp * cp * sl * sl / C + D * cp * cl * sp * sp;
                 f2p = sp * sp * cl / C + D * sl * sl * cp;
                 f2l = 0.5 * (sp * cp * sl / C - D * sp * cp * cp * sl * cl);
-                if (Q->mode) { /* Winkel Tripel */
+                if (Q->mode == WINKEL_TRIPEL) {
                 f1 = 0.5 * (f1 + lp.lam * Q->cosphi1);
                 f2 = 0.5 * (f2 + lp.phi);
                 f1p *= 0.5;
@@ -128,7 +133,7 @@ static LP s_inverse (XY xy, PJ *P) {           /* Spheroidal, inverse */
         } while ((fabs(dp) > EPSILON || fabs(dl) > EPSILON) && (iter++ < MAXITER));
         if (lp.phi > M_PI_2) lp.phi -= 2.*(lp.phi-M_PI_2); /* correct if symmetrical solution for Aitoff */
         if (lp.phi < -M_PI_2) lp.phi -= 2.*(lp.phi+M_PI_2); /* correct if symmetrical solution for Aitoff */
-        if ((fabs(fabs(lp.phi) - M_PI_2) < EPSILON) && (!Q->mode)) lp.lam = 0.; /* if pole in Aitoff, return longitude of 0 */
+        if ((fabs(fabs(lp.phi) - M_PI_2) < EPSILON) && (Q->mode == AITOFF)) lp.lam = 0.; /* if pole in Aitoff, return longitude of 0 */
 
         /* calculate x,y coordinates with solution obtained */
         if((D = acos(cos(lp.phi) * cos(C = 0.5 * lp.lam))) != 0.0) {/* Aitoff */
@@ -167,7 +172,7 @@ PJ *PROJECTION(aitoff) {
         return pj_default_destructor(P, ENOMEM);
     P->opaque = Q;
 
-    Q->mode = 0;
+    Q->mode = AITOFF;
     return setup(P);
 }
 
@@ -178,7 +183,7 @@ PJ *PROJECTION(wintri) {
         return pj_default_destructor(P, ENOMEM);
     P->opaque = Q;
 
-    Q->mode = 1;
+    Q->mode = WINKEL_TRIPEL;
     if (pj_param(P->ctx, P->params, "tlat_1").i) {
         if ((Q->cosphi1 = cos(pj_param(P->ctx, P->params, "rlat_1").f)) == 0.)
             return pj_default_destructor (P, PJD_ERR_LAT_LARGER_THAN_90);
diff --git a/src/PJ_gnom.c b/src/PJ_gnom.c
index 2aedefec..e5822f4f 100644
--- a/src/PJ_gnom.c
+++ b/src/PJ_gnom.c
@@ -6,15 +6,18 @@
 PROJ_HEAD(gnom, "Gnomonic") "\n\tAzi, Sph.";
 
 #define EPS10  1.e-10
-#define N_POLE 0
-#define S_POLE 1
-#define EQUIT  2
-#define OBLIQ  3
+
+enum Mode {
+    N_POLE = 0,
+    S_POLE = 1,
+    EQUIT  = 2,
+    OBLIQ  = 3
+};
 
 struct pj_opaque {
     double  sinph0;
     double  cosph0;
-    int     mode;
+    enum Mode mode;
 };
 
 
diff --git a/src/PJ_imw_p.c b/src/PJ_imw_p.c
index 29ed3457..7fd31fbb 100644
--- a/src/PJ_imw_p.c
+++ b/src/PJ_imw_p.c
@@ -9,11 +9,17 @@ PROJ_HEAD(imw_p, "International Map of the World Polyconic")
 #define TOL 1e-10
 #define EPS 1e-10
 
+enum Mode {
+    NONE_IS_ZERO  =  0, /* phi_1 and phi_2 != 0 */
+    PHI_1_IS_ZERO =  1, /* phi_1 = 0 */
+    PHI_2_IS_ZERO = -1  /* phi_2 = 0 */
+};
+
 struct pj_opaque {
-    double  P, Pp, Q, Qp, R_1, R_2, sphi_1, sphi_2, C2; \
-    double  phi_1, phi_2, lam_1; \
-    double  *en; \
-    int mode; /* = 0, phi_1 and phi_2 != 0, = 1, phi_1 = 0, = -1 phi_2 = 0 */
+    double  P, Pp, Q, Qp, R_1, R_2, sphi_1, sphi_2, C2;
+    double  phi_1, phi_2, lam_1;
+    double  *en;
+    enum Mode mode;
 };
 
 
@@ -53,7 +59,7 @@ static XY loc_for(LP lp, PJ *P, double *yc) {
         C = sqrt(R * R - xa * xa);
         if (lp.phi < 0.) C = - C;
         C += ya - R;
-        if (Q->mode < 0) {
+        if (Q->mode == PHI_2_IS_ZERO) {
             xb = lp.lam;
             yb = Q->C2;
         } else {
@@ -61,7 +67,7 @@ static XY loc_for(LP lp, PJ *P, double *yc) {
             xb = Q->R_2 * sin(t);
             yb = Q->C2 + Q->R_2 * (1. - cos(t));
         }
-        if (Q->mode > 0) {
+        if (Q->mode == PHI_1_IS_ZERO) {
             xc = lp.lam;
             *yc = 0.;
         } else {
@@ -171,18 +177,18 @@ PJ *PROJECTION(imw_p) {
         else                sig = 8.;
         Q->lam_1 = sig * DEG_TO_RAD;
     }
-    Q->mode = 0;
+    Q->mode = NONE_IS_ZERO;
     if (Q->phi_1 != 0.0)
         xy(P, Q->phi_1, &x1, &y1, &Q->sphi_1, &Q->R_1);
     else {
-        Q->mode = 1;
+        Q->mode = PHI_1_IS_ZERO;
         y1 = 0.;
         x1 = Q->lam_1;
     }
     if (Q->phi_2 != 0.0)
         xy(P, Q->phi_2, &x2, &T2, &Q->sphi_2, &Q->R_2);
     else {
-        Q->mode = -1;
+        Q->mode = PHI_2_IS_ZERO;
         T2 = 0.;
         x2 = Q->lam_1;
     }
diff --git a/src/PJ_laea.c b/src/PJ_laea.c
index 270b8dc8..0c5d5db9 100644
--- a/src/PJ_laea.c
+++ b/src/PJ_laea.c
@@ -5,6 +5,13 @@
 
 PROJ_HEAD(laea, "Lambert Azimuthal Equal Area") "\n\tAzi, Sph&Ell";
 
+enum Mode {
+    N_POLE = 0,
+    S_POLE = 1,
+    EQUIT  = 2,
+    OBLIQ  = 3
+};
+
 struct pj_opaque {
     double sinb1;
     double cosb1;
@@ -15,16 +22,12 @@ struct pj_opaque {
     double dd;
     double rq;
     double *apa;
-    int mode;
+    enum Mode mode;
 };
 
 #define EPS10   1.e-10
 #define NITER   20
 #define CONV    1.e-10
-#define N_POLE  0
-#define S_POLE  1
-#define EQUIT   2
-#define OBLIQ   3
 
 static XY e_forward (LP lp, PJ *P) {          /* Ellipsoidal, forward */
     XY xy = {0.0,0.0};
diff --git a/src/PJ_nsper.c b/src/PJ_nsper.c
index 4975bb17..6c8ef74a 100644
--- a/src/PJ_nsper.c
+++ b/src/PJ_nsper.c
@@ -3,6 +3,13 @@
 #include <proj.h>
 #include "projects.h"
 
+enum Mode {
+    N_POLE = 0,
+    S_POLE = 1,
+    EQUIT  = 2,
+    OBLIQ  = 3
+};
+
 struct pj_opaque {
     double  height;
     double  sinph0;
@@ -16,7 +23,7 @@ struct pj_opaque {
     double  sg;
     double  sw;
     double  cw;
-    int     mode;
+    enum Mode mode;
     int     tilt;
 };
 
@@ -24,10 +31,6 @@ PROJ_HEAD(nsper, "Near-sided perspective") "\n\tAzi, Sph\n\th=";
 PROJ_HEAD(tpers, "Tilted perspective") "\n\tAzi, Sph\n\ttilt= azi= h=";
 
 # define EPS10 1.e-10
-# define N_POLE 0
-# define S_POLE 1
-# define EQUIT  2
-# define OBLIQ  3
 
 
 static XY s_forward (LP lp, PJ *P) {           /* Spheroidal, forward */
diff --git a/src/PJ_ortho.c b/src/PJ_ortho.c
index 3179189b..14e228f7 100644
--- a/src/PJ_ortho.c
+++ b/src/PJ_ortho.c
@@ -5,17 +5,20 @@
 
 PROJ_HEAD(ortho, "Orthographic") "\n\tAzi, Sph.";
 
+enum Mode {
+    N_POLE = 0,
+    S_POLE = 1,
+    EQUIT  = 2,
+    OBLIQ  = 3
+};
+
 struct pj_opaque {
     double  sinph0;
     double  cosph0;
-    int     mode;
+    enum Mode mode;
 };
 
 #define EPS10 1.e-10
-#define N_POLE  0
-#define S_POLE 1
-#define EQUIT   2
-#define OBLIQ   3
 
 
 static XY s_forward (LP lp, PJ *P) {           /* Spheroidal, forward */
diff --git a/src/PJ_qsc.c b/src/PJ_qsc.c
index f8c760a9..f30a7048 100644
--- a/src/PJ_qsc.c
+++ b/src/PJ_qsc.c
@@ -42,8 +42,18 @@
 #include <errno.h>
 #include "projects.h"
 
+/* The six cube faces. */
+enum Face {
+    FACE_FRONT  = 0,
+    FACE_RIGHT  = 1,
+    FACE_BACK   = 2,
+    FACE_LEFT   = 3,
+    FACE_TOP    = 4,
+    FACE_BOTTOM = 5
+};
+
 struct pj_opaque {
-        int face;
+        enum Face face;
         double a_squared;
         double b;
         double one_minus_f;
@@ -53,24 +63,18 @@ PROJ_HEAD(qsc, "Quadrilateralized Spherical Cube") "\n\tAzi, Sph.";
 
 #define EPS10 1.e-10
 
-/* The six cube faces. */
-#define FACE_FRONT  0
-#define FACE_RIGHT  1
-#define FACE_BACK   2
-#define FACE_LEFT   3
-#define FACE_TOP    4
-#define FACE_BOTTOM 5
-
 /* The four areas on a cube face. AREA_0 is the area of definition,
  * the other three areas are counted counterclockwise. */
-#define AREA_0 0
-#define AREA_1 1
-#define AREA_2 2
-#define AREA_3 3
+enum Area {
+    AREA_0 = 0,
+    AREA_1 = 1,
+    AREA_2 = 2,
+    AREA_3 = 3
+};
 
 /* Helper function for forward projection: compute the theta angle
  * and determine the area number. */
-static double qsc_fwd_equat_face_theta(double phi, double y, double x, int *area) {
+static double qsc_fwd_equat_face_theta(double phi, double y, double x, enum Area *area) {
     double theta;
     if (phi < EPS10) {
         *area = AREA_0;
@@ -111,7 +115,7 @@ static XY e_forward (LP lp, PJ *P) {          /* Ellipsoidal, forward */
     double lat, lon;
     double theta, phi;
     double t, mu; /* nu; */
-    int area;
+    enum Area area;
 
     /* Convert the geodetic latitude to a geocentric latitude.
      * This corresponds to the shift from the ellipsoid to the sphere
diff --git a/src/PJ_sconics.c b/src/PJ_sconics.c
index 7f6e094c..b434c430 100644
--- a/src/PJ_sconics.c
+++ b/src/PJ_sconics.c
@@ -4,23 +4,26 @@
 #include "projects.h"
 
 
+enum Type {
+    EULER  = 0,
+    MURD1  = 1,
+    MURD2  = 2,
+    MURD3  = 3,
+    PCONIC = 4,
+    TISSOT = 5,
+    VITK1  = 6
+};
+
 struct pj_opaque {
     double  n;
     double  rho_c;
     double  rho_0;
     double  sig;
     double  c1, c2;
-    int     type;
+    enum Type type;
 };
 
 
-#define EULER 0
-#define MURD1 1
-#define MURD2 2
-#define MURD3 3
-#define PCONIC 4
-#define TISSOT 5
-#define VITK1 6
 #define EPS10   1.e-10
 #define EPS 1e-10
 #define LINE2 "\n\tConic, Sph\n\tlat_1= and lat_2="
@@ -106,7 +109,7 @@ static LP s_inverse (XY xy, PJ *P) {  /* Spheroidal, (and ellipsoidal?) inverse
 }
 
 
-static PJ *setup(PJ *P, int type) {
+static PJ *setup(PJ *P, enum Type type) {
     double del, cs;
     int err;
     struct pj_opaque *Q = pj_calloc (1, sizeof (struct pj_opaque));
diff --git a/src/PJ_stere.c b/src/PJ_stere.c
index 02b73507..500b512d 100644
--- a/src/PJ_stere.c
+++ b/src/PJ_stere.c
@@ -7,12 +7,19 @@ PROJ_HEAD(stere, "Stereographic") "\n\tAzi, Sph&Ell\n\tlat_ts=";
 PROJ_HEAD(ups, "Universal Polar Stereographic") "\n\tAzi, Sph&Ell\n\tsouth";
 
 
+enum Mode {
+    S_POLE = 0,
+    N_POLE = 1,
+    OBLIQ  = 2,
+    EQUIT  = 3
+};
+
 struct pj_opaque {
     double phits;
     double sinX1;
     double cosX1;
     double akm1;
-    int mode;
+    enum Mode mode;
 };
 
 #define sinph0  P->opaque->sinX1
@@ -21,10 +28,6 @@ struct pj_opaque {
 #define TOL 1.e-8
 #define NITER   8
 #define CONV    1.e-10
-#define S_POLE  0
-#define N_POLE  1
-#define OBLIQ   2
-#define EQUIT   3
 
 static double ssfn_ (double phit, double sinphi, double eccen) {
     sinphi *= eccen;