feat: algo/numeric/bin_search_integer.hpp

src/armkn/algo/numeric/bin_search_integer.hpp

@@ -0,0 +1,42 @@
+#pragma once
+#include <cstddef>
+#include <iostream>
+#include <type_traits>
+#include <utility>
+
+/// `p(ok)` を満たし、かつ `ng_` に最も近い `ok` を二分探索で求める。
+/// - 戻り値の値域は `min(ok_,ng_) - 1  <=  ok <= max(ok_,ng_) + 1`
+/// - `p(x) == true`  (`∀x ∈ [ok_, ng_]`) ならば `ng_` を返す。
+/// - `p(x) == false` (`∀x ∈ [ok_, ng_]`) ならば `[ok_, ng_]` の範囲外で `ok_` に最も近い値を返す。
+template <
+    class Int,
+    class PredicateFn,
+    class SignedInt = std::make_signed_t<Int>,
+    std::enable_if_t<std::is_integral_v<Int>, std::nullptr_t> = nullptr>
+SignedInt bin_search_integer(const Int ok_, const Int ng_, PredicateFn&& p) {
+  SignedInt ng, ok;
+  if (ng_ < ok_) {
+    ng = ng_ - 1;
+    ok = ok_ + 1;
+    while (ok - ng > 1) {
+      auto mid = ng + ((ok - ng) >> 1);
+      (p((Int)mid) ? ok : ng) = mid;
+    }
+  } else {
+    ng = ng_ + 1;
+    ok = ok_ - 1;
+    while (ng - ok > 1) {
+      auto mid = ok + ((ng - ok) >> 1);
+      (p((Int)mid) ? ok : ng) = mid;
+    }
+  }
+
+#ifdef ARMKN_DEBUG
+  if (ng == (SignedInt)ok_) {
+    std::clog << "\x1b[31;1m[Warn] ALL p(x) made FALSE\x1b[;m";
+    std::clog << "  initial range: (ok_,ng_)=(" << ok_ << ", " << ng_ << ") / result: (ok,ng)=("
+              << ok << ", " << ng << ')' << std::endl;
+  }
+#endif
+  return ok;
+}

tests/CMakeLists.txt

@@ -15,6 +15,7 @@ add_executable(tests
   armkn/algo/mapping/cycle_finder.cpp
   armkn/algo/mapping/doubling.cpp
   armkn/algo/mapping/doubling_with_monoid.cpp
+  armkn/algo/numeric/bin_search_integer.cpp
   armkn/dp/k_choose_prod_sum.cpp
   armkn/dsu/union_find.cpp
   armkn/fmt/printer.cpp

tests/armkn/algo/numeric/bin_search_integer.cpp

@@ -0,0 +1,28 @@
+#include <armkn/algo/numeric/bin_search_integer.hpp>
+#include <armkn/util/alias/stdint.hpp>
+#include <catch2/catch_test_macros.hpp>
+
+#include <utility>
+#include <vector>
+
+#define fn(expr) ([&](u32 i) { return (expr); })
+
+TEST_CASE("bin_search_integer") {
+  std::vector<int> a{1, 3, 3, 3, 3, 6};
+
+  CHECK(bin_search_integer(5u, 0u, fn(a[i] >= 1)) == 0);
+  CHECK(bin_search_integer(5u, 0u, fn(a[i] >= 2)) == 1);
+  CHECK(bin_search_integer(5u, 0u, fn(a[i] >= 3)) == 1);
+  CHECK(bin_search_integer(5u, 0u, fn(a[i] >= 4)) == 5);
+  CHECK(bin_search_integer(5u, 0u, fn(a[i] >= 5)) == 5);
+  CHECK(bin_search_integer(5u, 0u, fn(a[i] >= 6)) == 5);
+  CHECK(bin_search_integer(5u, 0u, fn(a[i] >= 7)) == 6);
+
+  CHECK(bin_search_integer(0u, 5u, fn(a[i] < 1)) == -1);
+  CHECK(bin_search_integer(0u, 5u, fn(a[i] < 2)) == 0);
+  CHECK(bin_search_integer(0u, 5u, fn(a[i] < 3)) == 0);
+  CHECK(bin_search_integer(0u, 5u, fn(a[i] < 4)) == 4);
+  CHECK(bin_search_integer(0u, 5u, fn(a[i] < 5)) == 4);
+  CHECK(bin_search_integer(0u, 5u, fn(a[i] < 6)) == 4);
+  CHECK(bin_search_integer(0u, 5u, fn(a[i] < 7)) == 5);
+}