diff --git a/src/bignum/bignum.cc b/src/bignum/bignum.cc
new file mode 100644
index 0000000..6a1f62c
--- /dev/null
+++ b/src/bignum/bignum.cc
@@ -0,0 +1,37 @@
+#include "bignum.hh"
+
+#include <algorithm>
+
+#include <cmath>
+
+namespace abacus::bignum {
+
+BigNum::BigNum(std::int64_t number) {
+    if (number == 0) {
+        return;
+    }
+
+    if (number < 0) {
+        sign_ = -1;
+    } else {
+        sign_ = 1;
+    }
+
+    auto abs = static_cast<std::uint64_t>(std::abs(number));
+    do {
+        digits_.push_back(abs % 10);
+        abs /= 10;
+    } while (abs);
+}
+
+void BigNum::canonicalize() {
+    auto const it = std::find_if(digits_.rbegin(), digits_.rend(),
+                                 [](auto v) { return v != 0; });
+    digits_.erase(it.base(), digits_.end());
+
+    if (digits_.size() == 0) {
+        sign_ = 0;
+    }
+}
+
+} // namespace abacus::bignum
diff --git a/src/bignum/bignum.hh b/src/bignum/bignum.hh
new file mode 100644
index 0000000..54db82b
--- /dev/null
+++ b/src/bignum/bignum.hh
@@ -0,0 +1,20 @@
+#pragma once
+
+#include <vector>
+
+#include <cstdint>
+
+namespace abacus::bignum {
+
+class BigNum {
+public:
+    explicit BigNum(std::int64_t number);
+
+private:
+    void canonicalize();
+
+    std::vector<std::uint8_t> digits_{};
+    int sign_ = 0;
+};
+
+} // namespace abacus::bignum
diff --git a/src/bignum/meson.build b/src/bignum/meson.build
new file mode 100644
index 0000000..7346d21
--- /dev/null
+++ b/src/bignum/meson.build
@@ -0,0 +1,16 @@
+bignum_sources = files(
+  'bignum.cc',
+  'bignum.hh',
+)
+
+bignum_inc = include_directories('.')
+
+bignum_lib = library(
+  'bignum',
+  sources: bignum_sources,
+)
+
+bignum = declare_dependency(
+  link_with: bignum_lib,
+  include_directories: bignum_inc,
+)
diff --git a/src/meson.build b/src/meson.build
index da90f6c..50721d2 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -2,6 +2,7 @@ abacus_sources = files(
   'abacus.cc',
 )
 
+subdir('bignum')
 subdir('parse')
 
 abacus = executable(