add lowlatency and lowuop template tags to modular_addition and modular_subtraction, and improve the experimental montgomery_pow_kary and montgomery_two_pow

Author: Jeffrey Hurchalla

modular_arithmetic/CMakeLists.txt

@@ -1,4 +1,4 @@
-# Copyright (c) 2020-2022 Jeffrey Hurchalla.
+# Copyright (c) 2020-2025 Jeffrey Hurchalla.
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at https://mozilla.org/MPL/2.0/.
@@ -47,6 +47,7 @@ target_sources(hurchalla_basic_modular_arithmetic INTERFACE
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/hurchalla/modular_arithmetic/modular_subtraction.h>
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/hurchalla/modular_arithmetic/detail/impl_modular_multiplicative_inverse.h>
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/hurchalla/modular_arithmetic/detail/impl_modular_pow.h>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/hurchalla/modular_arithmetic/detail/optimization_tag_structs.h>
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/hurchalla/modular_arithmetic/detail/platform_specific/impl_absolute_value_difference.h>
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/hurchalla/modular_arithmetic/detail/platform_specific/impl_modular_addition.h>
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include/hurchalla/modular_arithmetic/detail/platform_specific/impl_modular_multiplication.h>

modular_arithmetic/include/hurchalla/modular_arithmetic/absolute_value_difference.h

@@ -1,4 +1,4 @@
-// Copyright (c) 2020-2022 Jeffrey Hurchalla.
+// Copyright (c) 2020-2025 Jeffrey Hurchalla.
 /*
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
@@ -11,20 +11,16 @@
 
 #include "hurchalla/modular_arithmetic/detail/platform_specific/impl_absolute_value_difference.h"
 #include "hurchalla/util/traits/ut_numeric_limits.h"
+#include "hurchalla/util/compiler_macros.h"
 #include "hurchalla/util/programming_by_contract.h"
 
 namespace hurchalla {
 
 
-// Performance note:
-//   On some systems, this function may perform better when T is signed than
-// when it is unsigned.  Specifically, when HURCHALLA_AVOID_CSELECT is defined
-// (see hurchalla/util/compiler_macros.h) a signed type can perform better; if
-// it is not defined you should expect no performance difference between signed
-// and unsigned.
+// This function returns absolute_value(a-b), calculated as if 'a' and 'b' are
+// infinite precision signed integers.  It requires a>=0 and b>=0.
 
-
-template <typename T>
+template <typename T>  HURCHALLA_FORCE_INLINE
 T absolute_value_difference(T a, T b)
 {
     static_assert(ut_numeric_limits<T>::is_integer, "");
@@ -39,6 +35,15 @@ T absolute_value_difference(T a, T b)
 }
 
 
+// Performance note for RISC-V (and other uncommon CPU architectures that do not
+// have an instruction for conditional move or conditional select):
+//   On this architecture, this function may perform better when T is signed
+// than when it is unsigned.  Specifically, when HURCHALLA_AVOID_CSELECT is
+// defined (see hurchalla/util/compiler_macros.h), a signed type may perform
+// better; if it is not defined, you should expect no performance difference
+// between signed and unsigned.
+
+
 }  // end namespace
 
 #endif

…low_level_api/optimization_tag_structs.h …hmetic/detail/optimization_tag_structs.hmontgomery_arithmetic/include/hurchalla/montgomery_arithmetic/low_level_api/optimization_tag_structs.h renamed to modular_arithmetic/include/hurchalla/modular_arithmetic/detail/optimization_tag_structs.h montgomery_arithmetic/include/hurchalla/montgomery_arithmetic/low_level_api/optimization_tag_structs.h renamed to modular_arithmetic/include/hurchalla/modular_arithmetic/detail/optimization_tag_structs.h

@@ -1,12 +1,12 @@
-// Copyright (c) 2020-2022 Jeffrey Hurchalla.
+// Copyright (c) 2020-2025 Jeffrey Hurchalla.
 /*
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/.
  */
 
-#ifndef HURCHALLA_MONTGOMERY_ARITHMETIC_OPTIMIZATION_TAG_STRUCTS_H_INCLUDED
-#define HURCHALLA_MONTGOMERY_ARITHMETIC_OPTIMIZATION_TAG_STRUCTS_H_INCLUDED
+#ifndef HURCHALLA_MODULAR_ARITHMETIC_OPTIMIZATION_TAG_STRUCTS_H_INCLUDED
+#define HURCHALLA_MODULAR_ARITHMETIC_OPTIMIZATION_TAG_STRUCTS_H_INCLUDED
 
 
 namespace hurchalla {

modular_arithmetic/include/hurchalla/modular_arithmetic/detail/platform_specific/impl_absolute_value_difference.h

@@ -1,4 +1,4 @@
-// Copyright (c) 2020-2022 Jeffrey Hurchalla.
+// Copyright (c) 2020-2025 Jeffrey Hurchalla.
 /*
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
@@ -19,7 +19,9 @@
 namespace hurchalla { namespace detail {
 
 
-// note: uses a static member function to disallow ADL.
+// Fyi: the purpose of having structs with static member functions is to
+// disallow ADL and to make specializations simple and easy.
+
 struct default_impl_absdiff_unsigned {
   template <typename T>
   HURCHALLA_FORCE_INLINE static T call(T a, T b)
@@ -63,7 +65,11 @@ struct impl_absolute_value_difference_unsigned<std::uint32_t> {
     __asm__ ("subl %[b], %[tmp] \n\t"       /* tmp = a - b */
              "cmovbl %[diff], %[tmp] \n\t"  /* tmp = (a < b) ? diff : tmp */
              : [tmp]"+&r"(tmp)
+# if defined(__clang__)        /* https://bugs.llvm.org/show_bug.cgi?id=20197 */
              : [b]"r"(b), [diff]"r"(diff)
+# else
+             : [b]"rm"(b), [diff]"rm"(diff)
+# endif
              : "cc");
     uint32_t result = tmp;
 
@@ -84,7 +90,11 @@ struct impl_absolute_value_difference_unsigned<std::uint64_t> {
     __asm__ ("subq %[b], %[tmp] \n\t"       /* tmp = a - b */
              "cmovbq %[diff], %[tmp] \n\t"  /* tmp = (a < b) ? diff : tmp */
              : [tmp]"+&r"(tmp)
+# if defined(__clang__)        /* https://bugs.llvm.org/show_bug.cgi?id=20197 */
              : [b]"r"(b), [diff]"r"(diff)
+# else
+             : [b]"rm"(b), [diff]"rm"(diff)
+# endif
              : "cc");
     uint64_t result = tmp;
 
@@ -94,6 +104,41 @@ struct impl_absolute_value_difference_unsigned<std::uint64_t> {
   }
 };
 
+#ifdef HURCHALLA_ENABLE_INLINE_ASM_128_BIT
+template <>
+struct impl_absolute_value_difference_unsigned<__uint128_t> {
+  HURCHALLA_FORCE_INLINE
+  static __uint128_t call(__uint128_t a, __uint128_t b)
+  {
+    using std::uint64_t;
+    __uint128_t diff = static_cast<__uint128_t>(b - a);
+
+    uint64_t alo = static_cast<uint64_t>(a);
+    uint64_t ahi = static_cast<uint64_t>(a >> 64);
+    uint64_t difflo = static_cast<uint64_t>(diff);
+    uint64_t diffhi = static_cast<uint64_t>(diff >> 64);
+    uint64_t blo = static_cast<uint64_t>(b);
+    uint64_t bhi = static_cast<uint64_t>(b >> 64);
+    __asm__ ("subq %[blo], %[alo] \n\t"       /* tmp = a - b */
+             "sbbq %[bhi], %[ahi] \n\t"
+             "cmovbq %[difflo], %[alo] \n\t"  /* tmp = (a < b) ? diff : tmp */
+             "cmovbq %[diffhi], %[ahi] \n\t"
+             : [alo]"+&r"(alo), [ahi]"+&r"(ahi)
+# if defined(__clang__)        /* https://bugs.llvm.org/show_bug.cgi?id=20197 */
+             : [blo]"r"(blo), [bhi]"r"(bhi), [difflo]"r"(difflo), [diffhi]"r"(diffhi)
+# else
+             : [blo]"rm"(blo), [bhi]"rm"(bhi), [difflo]"rm"(difflo), [diffhi]"rm"(diffhi)
+# endif
+             : "cc");
+    __uint128_t result = (static_cast<__uint128_t>(ahi) << 64) | alo;
+
+    HPBC_POSTCONDITION2(result<=a || result<=b);
+    HPBC_POSTCONDITION2(result == default_impl_absdiff_unsigned::call(a, b));
+    return result;
+  }
+};
+#endif
+
 #endif