From ef020de16fda6b11c95abce6a565da8a2d373b52 Mon Sep 17 00:00:00 2001
From: Tim Ruffing <crypto@timruffing.de>
Date: Mon, 22 Oct 2018 16:23:09 +0200
Subject: [PATCH] Add size constants for preallocated memory

---
 src/ecmult.h          |  1 +
 src/ecmult_gen.h      |  1 +
 src/ecmult_gen_impl.h |  8 ++++++++
 src/ecmult_impl.h     | 10 +++++++++-
 src/secp256k1.c       | 18 ++++++++++++++++++
 5 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/src/ecmult.h b/src/ecmult.h
index 3d75a960f4247..6ac78bc3e6ca7 100644
--- a/src/ecmult.h
+++ b/src/ecmult.h
@@ -20,6 +20,7 @@ typedef struct {
 #endif
 } secp256k1_ecmult_context;
 
+static const size_t SECP256K1_ECMULT_CONTEXT_PREALLOCATED_SIZE;
 static void secp256k1_ecmult_context_init(secp256k1_ecmult_context *ctx);
 static void secp256k1_ecmult_context_build(secp256k1_ecmult_context *ctx, const secp256k1_callback *cb);
 static void secp256k1_ecmult_context_clone(secp256k1_ecmult_context *dst,
diff --git a/src/ecmult_gen.h b/src/ecmult_gen.h
index 7564b7015f0b7..0e23bc1095a7c 100644
--- a/src/ecmult_gen.h
+++ b/src/ecmult_gen.h
@@ -28,6 +28,7 @@ typedef struct {
     secp256k1_gej initial;
 } secp256k1_ecmult_gen_context;
 
+static const size_t SECP256K1_ECMULT_GEN_CONTEXT_PREALLOCATED_SIZE;
 static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context* ctx);
 static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context* ctx, const secp256k1_callback* cb);
 static void secp256k1_ecmult_gen_context_clone(secp256k1_ecmult_gen_context *dst,
diff --git a/src/ecmult_gen_impl.h b/src/ecmult_gen_impl.h
index d64505dc00107..1188a21367683 100644
--- a/src/ecmult_gen_impl.h
+++ b/src/ecmult_gen_impl.h
@@ -7,6 +7,7 @@
 #ifndef SECP256K1_ECMULT_GEN_IMPL_H
 #define SECP256K1_ECMULT_GEN_IMPL_H
 
+#include "util.h"
 #include "scalar.h"
 #include "group.h"
 #include "ecmult_gen.h"
@@ -14,6 +15,13 @@
 #ifdef USE_ECMULT_STATIC_PRECOMPUTATION
 #include "ecmult_static_context.h"
 #endif
+
+#ifndef USE_ECMULT_STATIC_PRECOMPUTATION
+    static const size_t SECP256K1_ECMULT_GEN_CONTEXT_PREALLOCATED_SIZE = ROUND_TO_ALIGN(sizeof(*((secp256k1_ecmult_gen_context*) NULL)->prec));
+#else
+    static const size_t SECP256K1_ECMULT_GEN_CONTEXT_PREALLOCATED_SIZE = 0;
+#endif
+
 static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context *ctx) {
     ctx->prec = NULL;
 }
diff --git a/src/ecmult_impl.h b/src/ecmult_impl.h
index a93a0df3b416d..70db458406c92 100644
--- a/src/ecmult_impl.h
+++ b/src/ecmult_impl.h
@@ -10,6 +10,7 @@
 #include <string.h>
 #include <stdint.h>
 
+#include "util.h"
 #include "group.h"
 #include "scalar.h"
 #include "ecmult.h"
@@ -310,6 +311,13 @@ static void secp256k1_ecmult_odd_multiples_table_storage_var(const int n, secp25
     } \
 } while(0)
 
+static const size_t SECP256K1_ECMULT_CONTEXT_PREALLOCATED_SIZE =
+    ROUND_TO_ALIGN(sizeof((*((secp256k1_ecmult_context*) NULL)->pre_g)[0]) * ECMULT_TABLE_SIZE(WINDOW_G))
+#ifdef USE_ENDOMORPHISM
+    + ROUND_TO_ALIGN(sizeof((*((secp256k1_ecmult_context*) NULL)->pre_g_128)[0]) * ECMULT_TABLE_SIZE(WINDOW_G))
+#endif
+    ;
+
 static void secp256k1_ecmult_context_init(secp256k1_ecmult_context *ctx) {
     ctx->pre_g = NULL;
 #ifdef USE_ENDOMORPHISM
@@ -442,7 +450,7 @@ static int secp256k1_ecmult_wnaf(int *wnaf, int len, const secp256k1_scalar *a,
     CHECK(carry == 0);
     while (bit < 256) {
         CHECK(secp256k1_scalar_get_bits(&s, bit++, 1) == 0);
-    } 
+    }
 #endif
     return last_set_bit + 1;
 }
diff --git a/src/secp256k1.c b/src/secp256k1.c
index 73adc6e020de6..fe936c53193d9 100644
--- a/src/secp256k1.c
+++ b/src/secp256k1.c
@@ -64,6 +64,24 @@ static const secp256k1_context secp256k1_context_no_precomp_ = {
 };
 const secp256k1_context *secp256k1_context_no_precomp = &secp256k1_context_no_precomp_;
 
+size_t secp256k1_context_preallocated_size(unsigned int flags) {
+    size_t ret = ROUND_TO_ALIGN(sizeof(secp256k1_context));
+
+    if (EXPECT((flags & SECP256K1_FLAGS_TYPE_MASK) != SECP256K1_FLAGS_TYPE_CONTEXT, 0)) {
+            secp256k1_callback_call(&default_illegal_callback,
+                                    "Invalid flags");
+            return 0;
+    }
+
+    if (flags & SECP256K1_FLAGS_BIT_CONTEXT_SIGN) {
+        ret += SECP256K1_ECMULT_GEN_CONTEXT_PREALLOCATED_SIZE;
+    }
+    if (flags & SECP256K1_FLAGS_BIT_CONTEXT_VERIFY) {
+        ret += SECP256K1_ECMULT_CONTEXT_PREALLOCATED_SIZE;
+    }
+    return ret;
+}
+
 secp256k1_context* secp256k1_context_create(unsigned int flags) {
     secp256k1_context* ret = (secp256k1_context*)checked_malloc(&default_error_callback, sizeof(secp256k1_context));
     ret->illegal_callback = default_illegal_callback;