AVX code: move stub into separate file; always check -mavx2/-mfma

This simplifies the build a bit by moving the avx stubs into a single .c
file: we can avoid compiling all of the avx2 code and just add a single
stub file instead when the compiler doesn't have -mavx2/-mfma.

This also simplifies cmake to just always test the flags; there are some
cases (like using NATIVE_BUILD) where USE_AVX2 doesn't necessarily
apply, and it's cheap to just check them.

crypto/CMakeLists.txt

@@ -42,20 +42,17 @@ set(NTRU_AVX_SRC
   libntrup/src/avx/rq.c
   libntrup/src/avx/rq_mod3.c
 )
-if(NOT NATIVE_BUILD AND USE_AVX2)
-  # Assume cxxflags are already enabling AVX2
+
+include(CheckCXXCompilerFlag)
+check_cxx_compiler_flag(-mavx2 COMPILER_SUPPORTS_AVX2)
+check_cxx_compiler_flag(-mfma COMPILER_SUPPORTS_FMA)
+if(COMPILER_SUPPORTS_AVX2 AND COMPILER_SUPPORTS_FMA)
   target_sources(lokinet-cryptography PRIVATE ${NTRU_AVX_SRC})
+  set_property(SOURCE ${NTRU_AVX_SRC} APPEND PROPERTY COMPILE_FLAGS "-mavx2 -mfma")
+  message(STATUS "Building libntrup with runtime AVX2/FMA support")
 else()
-  include(CheckCXXCompilerFlag)
-  check_cxx_compiler_flag(-mavx2 COMPILER_SUPPORTS_AVX2)
-  check_cxx_compiler_flag(-mfma COMPILER_SUPPORTS_FMA)
-  if(COMPILER_SUPPORTS_AVX2 AND COMPILER_SUPPORTS_FMA)
-    target_sources(lokinet-cryptography PRIVATE ${NTRU_AVX_SRC})
-    set_property(SOURCE ${NTRU_AVX_SRC} APPEND PROPERTY COMPILE_FLAGS "-mavx2 -mfma")
-    message(STATUS "Building libntrup with runtime AVX2/FMA support")
-  else()
-    message(STATUS "Not building with libntrup runtime AVX2/FMA support (can't figure out how to compile with AVX2/FMA: -mavx2 -mfma didn't work)")
-  endif()
+  target_sources(lokinet-cryptography PRIVATE libntrup/src/noavx-stubs.c)
+  message(STATUS "Not building with libntrup runtime AVX2/FMA support (either this architecture doesn't support them, or your compile doesn't support the -mavx2 -mfma flags")
 endif()
 
 enable_lto(lokinet-cryptography)

crypto/libntrup/src/avx/dec.c

@@ -11,11 +11,14 @@
 #include "rq.h"
 #include "r3.h"
 
+#ifndef __AVX2__
+#error "This file requires compilation with AVX2 support"
+#endif
+
 int
 crypto_kem_dec_avx2(unsigned char *k, const unsigned char *cstr,
                     const unsigned char *sk)
 {
-#if __AVX2__
   small f[768];
   modq h[768];
   small grecip[768];
@@ -67,10 +70,4 @@ crypto_kem_dec_avx2(unsigned char *k, const unsigned char *cstr,
   for(i = 0; i < 32; ++i)
     k[i] = (hash[32 + i] & ~result);
   return result;
-#else
-  (void)(k);
-  (void)(sk);
-  (void)(cstr);
-  return -1;
-#endif
 }

crypto/libntrup/src/avx/enc.c

@@ -9,11 +9,14 @@
 #include <sodium/crypto_hash_sha512.h>
 #include <sodium/crypto_kem.h>
 
+#ifndef __AVX2__
+#error "This file requires compilation with AVX2 support"
+#endif
+
 int
 crypto_kem_enc_avx2(unsigned char *cstr, unsigned char *k,
                     const unsigned char *pk)
 {
-#if __AVX2__
   small r[768];
   modq h[768];
   modq c[768];
@@ -46,10 +49,4 @@ crypto_kem_enc_avx2(unsigned char *cstr, unsigned char *k,
   rq_roundencode(cstr + 32, c);
 
   return 0;
-#else
-  (void)(cstr);
-  (void)(k);
-  (void)(pk);
-  return -1;
-#endif
 }

crypto/libntrup/src/avx/keypair.c

@@ -14,10 +14,13 @@
     "crypto_kem_SECRETKEYBYTES must match rq_encode_len + 2 * small_encode_len"
 #endif
 
+#ifndef __AVX2__
+#error "This file requires compilation with AVX2 support"
+#endif
+
 int
 crypto_kem_keypair_avx2(unsigned char *pk, unsigned char *sk)
 {
-#if __AVX2__
   small g[768];
   small grecip[768];
   small f[768];
@@ -39,9 +42,4 @@ crypto_kem_keypair_avx2(unsigned char *pk, unsigned char *sk)
   memcpy(sk + 2 * small_encode_len, pk, rq_encode_len);
 
   return 0;
-#else
-  (void)(pk);
-  (void)(sk);
-  return -1;
-#endif
 }

crypto/libntrup/src/noavx-stubs.c

@@ -0,0 +1,29 @@
+// Stubs for compilers/builds without avx2 support
+//
+int
+crypto_kem_enc_avx2(unsigned char *cstr, unsigned char *k,
+                    const unsigned char *pk)
+{
+  (void)(cstr);
+  (void)(k);
+  (void)(pk);
+  return -1;
+}
+
+int
+crypto_kem_dec_avx2(unsigned char *k, const unsigned char *cstr,
+                    const unsigned char *sk)
+{
+  (void)(k);
+  (void)(sk);
+  (void)(cstr);
+  return -1;
+}
+
+int
+crypto_kem_keypair_avx2(unsigned char *pk, unsigned char *sk)
+{
+  (void)(pk);
+  (void)(sk);
+  return -1;
+}

crypto/libntrup/src/ntru.cpp

@@ -43,14 +43,12 @@ extern "C"
     {
       __crypto_kem_dec     = &crypto_kem_dec_avx2;
       __crypto_kem_enc     = &crypto_kem_enc_avx2;
-      __crypto_kem_dec     = &crypto_kem_dec_avx2;
       __crypto_kem_keypair = &crypto_kem_keypair_avx2;
     }
     else
     {
       __crypto_kem_dec     = &crypto_kem_dec_ref;
       __crypto_kem_enc     = &crypto_kem_enc_ref;
-      __crypto_kem_dec     = &crypto_kem_dec_ref;
       __crypto_kem_keypair = &crypto_kem_keypair_ref;
     }
   }