1 files changed, 81 insertions, 0 deletions
diff --git a/src/secp256k1/src/ecmult_gen_prec_impl.h b/src/secp256k1/src/ecmult_gen_prec_impl.h
new file mode 100644
index 0000000000..bac76c8b13
--- /dev/null
+++ b/src/secp256k1/src/ecmult_gen_prec_impl.h
@@ -0,0 +1,81 @@
+/***********************************************************************
+ * Copyright (c) 2013, 2014, 2015 Pieter Wuille, Gregory Maxwell       *
+ * Distributed under the MIT software license, see the accompanying    *
+ * file COPYING or https://www.opensource.org/licenses/mit-license.php.*
+ ***********************************************************************/
+
+#ifndef SECP256K1_ECMULT_GEN_PREC_IMPL_H
+#define SECP256K1_ECMULT_GEN_PREC_IMPL_H
+
+#include "ecmult_gen_prec.h"
+#include "group_impl.h"
+#include "field_impl.h"
+#include "ecmult_gen.h"
+#include "util.h"
+
+static void secp256k1_ecmult_gen_create_prec_table(secp256k1_ge_storage* table, const secp256k1_ge* gen, int bits) {
+    int g = ECMULT_GEN_PREC_G(bits);
+    int n = ECMULT_GEN_PREC_N(bits);
+
+    secp256k1_ge* prec = checked_malloc(&default_error_callback, n * g * sizeof(*prec));
+    secp256k1_gej gj;
+    secp256k1_gej nums_gej;
+    int i, j;
+
+    /* get the generator */
+    secp256k1_gej_set_ge(&gj, gen);
+
+    /* Construct a group element with no known corresponding scalar (nothing up my sleeve). */
+    {
+        static const unsigned char nums_b32[33] = "The scalar for this x is unknown";
+        secp256k1_fe nums_x;
+        secp256k1_ge nums_ge;
+        int r;
+        r = secp256k1_fe_set_b32(&nums_x, nums_b32);
+        (void)r;
+        VERIFY_CHECK(r);
+        r = secp256k1_ge_set_xo_var(&nums_ge, &nums_x, 0);
+        (void)r;
+        VERIFY_CHECK(r);
+        secp256k1_gej_set_ge(&nums_gej, &nums_ge);
+        /* Add G to make the bits in x uniformly distributed. */
+        secp256k1_gej_add_ge_var(&nums_gej, &nums_gej, gen, NULL);
+    }
+
+    /* compute prec. */
+    {
+        secp256k1_gej gbase;
+        secp256k1_gej numsbase;
+        secp256k1_gej* precj = checked_malloc(&default_error_callback, n * g * sizeof(*precj));  /* Jacobian versions of prec. */
+        gbase = gj; /* PREC_G^j * G */
+        numsbase = nums_gej; /* 2^j * nums. */
+        for (j = 0; j < n; j++) {
+            /* Set precj[j*PREC_G .. j*PREC_G+(PREC_G-1)] to (numsbase, numsbase + gbase, ..., numsbase + (PREC_G-1)*gbase). */
+            precj[j*g] = numsbase;
+            for (i = 1; i < g; i++) {
+                secp256k1_gej_add_var(&precj[j*g + i], &precj[j*g + i - 1], &gbase, NULL);
+            }
+            /* Multiply gbase by PREC_G. */
+            for (i = 0; i < bits; i++) {
+                secp256k1_gej_double_var(&gbase, &gbase, NULL);
+            }
+            /* Multiply numbase by 2. */
+            secp256k1_gej_double_var(&numsbase, &numsbase, NULL);
+            if (j == n - 2) {
+                /* In the last iteration, numsbase is (1 - 2^j) * nums instead. */
+                secp256k1_gej_neg(&numsbase, &numsbase);
+                secp256k1_gej_add_var(&numsbase, &numsbase, &nums_gej, NULL);
+            }
+        }
+        secp256k1_ge_set_all_gej_var(prec, precj, n * g);
+        free(precj);
+    }
+    for (j = 0; j < n; j++) {
+        for (i = 0; i < g; i++) {
+            secp256k1_ge_to_storage(&table[j*g + i], &prec[j*g + i]);
+        }
+    }
+    free(prec);
+}
+
+#endif /* SECP256K1_ECMULT_GEN_PREC_IMPL_H */