Import ed25519 implementation from https://github.com/orlp/ed25519

Externals/ed25519/ge.h

@@ -0,0 +1,74 @@
+#ifndef GE_H
+#define GE_H
+
+#include "fe.h"
+
+
+/*
+ge means group element.
+
+Here the group is the set of pairs (x,y) of field elements (see fe.h)
+satisfying -x^2 + y^2 = 1 + d x^2y^2
+where d = -121665/121666.
+
+Representations:
+  ge_p2 (projective): (X:Y:Z) satisfying x=X/Z, y=Y/Z
+  ge_p3 (extended): (X:Y:Z:T) satisfying x=X/Z, y=Y/Z, XY=ZT
+  ge_p1p1 (completed): ((X:Z),(Y:T)) satisfying x=X/Z, y=Y/T
+  ge_precomp (Duif): (y+x,y-x,2dxy)
+*/
+
+typedef struct {
+  fe X;
+  fe Y;
+  fe Z;
+} ge_p2;
+
+typedef struct {
+  fe X;
+  fe Y;
+  fe Z;
+  fe T;
+} ge_p3;
+
+typedef struct {
+  fe X;
+  fe Y;
+  fe Z;
+  fe T;
+} ge_p1p1;
+
+typedef struct {
+  fe yplusx;
+  fe yminusx;
+  fe xy2d;
+} ge_precomp;
+
+typedef struct {
+  fe YplusX;
+  fe YminusX;
+  fe Z;
+  fe T2d;
+} ge_cached;
+
+void ge_p3_tobytes(unsigned char *s, const ge_p3 *h);
+void ge_tobytes(unsigned char *s, const ge_p2 *h);
+int ge_frombytes_negate_vartime(ge_p3 *h, const unsigned char *s);
+
+void ge_add(ge_p1p1 *r, const ge_p3 *p, const ge_cached *q);
+void ge_sub(ge_p1p1 *r, const ge_p3 *p, const ge_cached *q);
+void ge_double_scalarmult_vartime(ge_p2 *r, const unsigned char *a, const ge_p3 *A, const unsigned char *b);
+void ge_madd(ge_p1p1 *r, const ge_p3 *p, const ge_precomp *q);
+void ge_msub(ge_p1p1 *r, const ge_p3 *p, const ge_precomp *q);
+void ge_scalarmult_base(ge_p3 *h, const unsigned char *a);
+
+void ge_p1p1_to_p2(ge_p2 *r, const ge_p1p1 *p);
+void ge_p1p1_to_p3(ge_p3 *r, const ge_p1p1 *p);
+void ge_p2_0(ge_p2 *h);
+void ge_p2_dbl(ge_p1p1 *r, const ge_p2 *p);
+void ge_p3_0(ge_p3 *h);
+void ge_p3_dbl(ge_p1p1 *r, const ge_p3 *p);
+void ge_p3_to_cached(ge_cached *r, const ge_p3 *p);
+void ge_p3_to_p2(ge_p2 *r, const ge_p3 *p);
+
+#endif