(stdlib) Replace BigInt library with libtommath implementation

The previous C++-based implementation used strings for storing its
values. The new approach uses a C-based library which is much more
performant.

README.md

@@ -128,7 +128,7 @@ guide.
 
 ## License
 
-[MIT](LICENSE)
+[MIT (Expat)](LICENSE)
 
 [perlang-install](scripts/perlang-install) is originally based on
 [rustup-init](https://github.com/rust-lang/rustup/blob/master/rustup-init.sh),
@@ -151,6 +151,10 @@ Syed Faheel Ahmad's `BigInt` library, available at
 https://github.com/faheel/BigInt, licensed under the terms of the MIT license.
 Copyright (c) 2017 - 2018 Syed Faheel Ahmad.
 
+[src/stdlib/src/libtommath](src/stdlib/src/libtommath/) includes content from
+libtommath (https://github.com/libtom/libtommath), licensed under the Unlicense
+(http://unlicense.org).
+
 [src/stdlib/src/double-conversion](src/stdlib/src/double-conversion) includes
 content from the Google `double-conversion` library, available at
 https://github.com/google/double-conversion, licensed under the BSD 3-Clause

release-notes/v0.4.0.md

@@ -12,6 +12,7 @@
 - Initial support for `**` operator in compiled mode [[#420][420]]
 - Use correct error message for unsupported operand types [[#421][421]]
 - Support `**` for `BigInt` values [[#422][422]]
+- Replace `BigInt` library with `libtommath` implementation [[#425][425]]
 
 ### Changed
 #### Data types
@@ -53,3 +54,4 @@
 [420]: https://github.com/perlang-org/perlang/pull/420
 [421]: https://github.com/perlang-org/perlang/pull/421
 [422]: https://github.com/perlang-org/perlang/pull/422
+[425]: https://github.com/perlang-org/perlang/pull/425

src/Perlang.Interpreter/Compiler/PerlangCompiler.cs

@@ -831,9 +831,6 @@ private void AddGlobalClass(string name, PerlangClass perlangClass)
                 if (new[] { typeof(int), typeof(long), typeof(uint), typeof(ulong), typeof(BigInteger) }.Contains(expr.Left.TypeReference.ClrType) &&
                     expr.Right.TypeReference.ClrType == typeof(int))
                 {
-                    // TODO: We need something lke BigInteger.Pow() in .NET to be able to accomplish this. Perhaps do
-                    // TODO: like the .NET folks and implement something using this approach?
-                    // TODO: https://en.wikipedia.org/wiki/Exponentiation_by_squaring
                     currentMethod.Append($"{leftCast}perlang::BigInt_pow({expr.Left.Accept(this)}, {rightCast}{expr.Right.Accept(this)})");
                 }
                 else if (new[] { typeof(int), typeof(long), typeof(uint), typeof(ulong), typeof(float), typeof(double) }.Contains(expr.Left.TypeReference.ClrType) &&

src/stdlib/CMakeLists.txt

@@ -7,12 +7,67 @@ set(headers
         src/double-conversion/utils.h
 )
 
+set(libtommath_headers
+        src/libtommath/tommath.h
+)
+
 add_library(
         stdlib
         src/bigint.cpp
         src/bigint_pow.cpp
         src/Base64.cpp
         src/print.cpp
+        src/libtommath/bn_cutoffs.c
+        src/libtommath/bn_mp_add.c
+        src/libtommath/bn_mp_clamp.c
+        src/libtommath/bn_mp_clear.c
+        src/libtommath/bn_mp_clear_multi.c
+        src/libtommath/bn_mp_cmp.c
+        src/libtommath/bn_mp_cmp_mag.c
+        src/libtommath/bn_mp_copy.c
+        src/libtommath/bn_mp_count_bits.c
+        src/libtommath/bn_mp_div.c
+        src/libtommath/bn_mp_div_d.c
+        src/libtommath/bn_mp_div_2.c
+        src/libtommath/bn_mp_div_2d.c
+        src/libtommath/bn_mp_div_3.c
+        src/libtommath/bn_mp_exch.c
+        src/libtommath/bn_mp_expt_u32.c
+        src/libtommath/bn_mp_grow.c
+        src/libtommath/bn_mp_init.c
+        src/libtommath/bn_mp_init_copy.c
+        src/libtommath/bn_mp_init_multi.c
+        src/libtommath/bn_mp_init_size.c
+        src/libtommath/bn_mp_lshd.c
+        src/libtommath/bn_mp_mod.c
+        src/libtommath/bn_mp_mod_2d.c
+        src/libtommath/bn_mp_mul.c
+        src/libtommath/bn_mp_mul_d.c
+        src/libtommath/bn_mp_mul_2.c
+        src/libtommath/bn_mp_mul_2d.c
+        src/libtommath/bn_mp_neg.c
+        src/libtommath/bn_mp_radix_size.c
+        src/libtommath/bn_mp_radix_smap.c
+        src/libtommath/bn_mp_rshd.c
+        src/libtommath/bn_mp_error_to_string.c
+        src/libtommath/bn_mp_to_radix.c
+        src/libtommath/bn_mp_set.c
+        src/libtommath/bn_mp_set_u64.c
+        src/libtommath/bn_mp_sqr.c
+        src/libtommath/bn_mp_sub.c
+        src/libtommath/bn_mp_zero.c
+        src/libtommath/bn_s_mp_add.c
+        src/libtommath/bn_s_mp_balance_mul.c
+        src/libtommath/bn_s_mp_karatsuba_mul.c
+        src/libtommath/bn_s_mp_karatsuba_sqr.c
+        src/libtommath/bn_s_mp_mul_digs.c
+        src/libtommath/bn_s_mp_mul_digs_fast.c
+        src/libtommath/bn_s_mp_sqr.c
+        src/libtommath/bn_s_mp_sqr_fast.c
+        src/libtommath/bn_s_mp_reverse.c
+        src/libtommath/bn_s_mp_sub.c
+        src/libtommath/bn_s_mp_toom_mul.c
+        src/libtommath/bn_s_mp_toom_sqr.c
 )
 
 # Enable C++ 17 support. This is required on e.g. AppleClang 13
@@ -46,6 +101,11 @@ install(
         DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
 )
 
+install(
+        FILES ${libtommath_headers}
+        DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/libtommath"
+)
+
 # The testing code is not yet ready for macOS, since it uses a different linker which doesn't support --wrap. We'll
 # live with only building/running the tests on other platforms for now.
 if (NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin")