batch: Initialize an experimental batch module

This commit adds the foundational configuration, build scripts,
and an initial structure for experimental batch module.

Makefile.am

@@ -227,3 +227,7 @@ endif
 if ENABLE_MODULE_SCHNORRSIG
 include src/modules/schnorrsig/Makefile.am.include
 endif
+
+if ENABLE_MODULE_BATCH
+include src/modules/batch/Makefile.am.include
+endif

README.md

@@ -21,6 +21,7 @@ Features:
 * Optional module for public key recovery.
 * Optional module for ECDH key exchange.
 * Optional module for Schnorr signatures according to [BIP-340](https://github.com/bitcoin/bips/blob/master/bip-0340.mediawiki).
+* Optional module for Batch Verification (experimental).
 
 Implementation details
 ----------------------

configure.ac

@@ -170,6 +170,10 @@ AC_ARG_ENABLE(module_schnorrsig,
     AS_HELP_STRING([--enable-module-schnorrsig],[enable schnorrsig module [default=no]]), [],
     [SECP_SET_DEFAULT([enable_module_schnorrsig], [no], [yes])])
 
+AC_ARG_ENABLE(module_batch,
+    AS_HELP_STRING([--enable-module-batch],[enable batch verification module (experimental) [default=no]]), [],
+    [SECP_SET_DEFAULT([enable_module_batch], [no], [yes])])
+
 AC_ARG_ENABLE(external_default_callbacks,
     AS_HELP_STRING([--enable-external-default-callbacks],[enable external default callback functions [default=no]]), [],
     [SECP_SET_DEFAULT([enable_external_default_callbacks], [no], [no])])
@@ -368,6 +372,10 @@ if test x"$enable_module_extrakeys" = x"yes"; then
   AC_DEFINE(ENABLE_MODULE_EXTRAKEYS, 1, [Define this symbol to enable the extrakeys module])
 fi
 
+if test x"$enable_module_batch" = x"yes"; then
+  AC_DEFINE(ENABLE_MODULE_BATCH, 1, [Define this symbol to enable the batch verification module])
+fi
+
 if test x"$enable_external_default_callbacks" = x"yes"; then
   AC_DEFINE(USE_EXTERNAL_DEFAULT_CALLBACKS, 1, [Define this symbol if an external implementation of the default callbacks is used])
 fi
@@ -380,11 +388,15 @@ if test x"$enable_experimental" = x"yes"; then
   AC_MSG_NOTICE([******])
   AC_MSG_NOTICE([WARNING: experimental build])
   AC_MSG_NOTICE([Experimental features do not have stable APIs or properties, and may not be safe for production use.])
+  AC_MSG_NOTICE([Building batch verification module: $enable_module_batch])
   AC_MSG_NOTICE([******])
 else
   if test x"$set_asm" = x"arm"; then
     AC_MSG_ERROR([ARM assembly optimization is experimental. Use --enable-experimental to allow.])
   fi
+  if test x"$enable_module_batch" = x"yes"; then
+    AC_MSG_ERROR([batch verification module is experimental. Use --enable-experimental to allow.])
+  fi
 fi
 
 ###
@@ -407,6 +419,7 @@ AM_CONDITIONAL([ENABLE_MODULE_ECDH], [test x"$enable_module_ecdh" = x"yes"])
 AM_CONDITIONAL([ENABLE_MODULE_RECOVERY], [test x"$enable_module_recovery" = x"yes"])
 AM_CONDITIONAL([ENABLE_MODULE_EXTRAKEYS], [test x"$enable_module_extrakeys" = x"yes"])
 AM_CONDITIONAL([ENABLE_MODULE_SCHNORRSIG], [test x"$enable_module_schnorrsig" = x"yes"])
+AM_CONDITIONAL([ENABLE_MODULE_BATCH], [test x"$enable_module_batch" = x"yes"])
 AM_CONDITIONAL([USE_EXTERNAL_ASM], [test x"$enable_external_asm" = x"yes"])
 AM_CONDITIONAL([USE_ASM_ARM], [test x"$set_asm" = x"arm"])
 AM_CONDITIONAL([BUILD_WINDOWS], [test "$build_windows" = "yes"])
@@ -427,6 +440,7 @@ echo "  module ecdh             = $enable_module_ecdh"
 echo "  module recovery         = $enable_module_recovery"
 echo "  module extrakeys        = $enable_module_extrakeys"
 echo "  module schnorrsig       = $enable_module_schnorrsig"
+echo "  module batch            = $enable_module_batch"
 echo
 echo "  asm                     = $set_asm"
 echo "  ecmult window size      = $set_ecmult_window"

include/secp256k1_batch.h

@@ -0,0 +1,25 @@
+#ifndef SECP256K1_BATCH_H
+#define SECP256K1_BATCH_H
+
+#include "secp256k1.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** This module implements a Batch Verification object that supports:
+ *
+ *  1. Schnorr signatures compliant with Bitcoin Improvement Proposal 340
+ *     "Schnorr Signatures for secp256k1"
+ *     (https://github.com/bitcoin/bips/blob/master/bip-0340.mediawiki).
+ *
+ *  2. Taproot commitments compliant with Bitcoin Improvemtn Proposal 341
+ *     "Taproot: SegWit version 1 spending rules"
+ *     (https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki).
+ */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SECP256K1_BATCH_H */

src/modules/batch/Makefile.am.include

@@ -0,0 +1,2 @@
+include_HEADERS += include/secp256k1_batch.h
+noinst_HEADERS += src/modules/batch/main_impl.h

src/modules/batch/main_impl.h

@@ -0,0 +1,6 @@
+#ifndef SECP256K1_MODULE_BATCH_MAIN_H
+#define SECP256K1_MODULE_BATCH_MAIN_H
+
+#include "include/secp256k1_batch.h"
+
+#endif /* SECP256K1_MODULE_BATCH_MAIN_H */

src/secp256k1.c

@@ -776,3 +776,7 @@ int secp256k1_tagged_sha256(const secp256k1_context* ctx, unsigned char *hash32,
 #ifdef ENABLE_MODULE_SCHNORRSIG
 # include "modules/schnorrsig/main_impl.h"
 #endif
+
+#ifdef ENABLE_MODULE_BATCH
+# include "modules/batch/main_impl.h"
+#endif