From 961e54c08b3c341321501988700cb8792a56bd09 Mon Sep 17 00:00:00 2001
From: SEK1RO <vlad@sek1.ro>
Date: Wed, 18 Sep 2024 23:29:21 +0300
Subject: [PATCH] feat(baseN): decode

---
 src/baseN.cpp       | 42 ++++++++++++++++++++++++++++++++++++++++++
 test/test-baseN.cpp | 27 ++++++++++++++-------------
 2 files changed, 56 insertions(+), 13 deletions(-)

diff --git a/src/baseN.cpp b/src/baseN.cpp
index 68d53b8..4614b79 100644
--- a/src/baseN.cpp
+++ b/src/baseN.cpp
@@ -84,4 +84,46 @@ namespace baseN
                                    { return ch != ' '; }));
         return str;
     }
+    void decode(const char *str, uint64_t str_size, uint8_t *data, uint64_t data_size, uint8_t base, const char *digits, const int8_t *map)
+    {
+        std::string_view sv(std::find_if(str, str + str_size, [digits](char ch)
+                                         { return ch != digits[0]; }),
+                            str_size);
+        if (sv.size() == 0)
+        {
+            return;
+        }
+        if (!baseN::isValid(sv, map))
+        {
+            throw std::logic_error("baseN::decode: out of digits map");
+        }
+        std::span<uint8_t> dv(data, data_size);
+        auto sv_it = sv.begin();
+        auto quo_it = dv.rbegin();
+        auto quo_it_last = dv.rbegin() + 1;
+        uint16_t div;
+
+        *quo_it = map[(int8_t)*sv_it++];
+        while (sv_it < sv.end())
+        {
+            div = map[(int8_t)*sv_it++];
+            while (quo_it < quo_it_last && quo_it < dv.rend() - 1)
+            {
+                div += *quo_it * base;
+                *quo_it++ = div;
+                div >>= 8;
+            }
+            *quo_it++ = div;
+            quo_it_last = quo_it;
+            quo_it = dv.rbegin();
+        }
+    }
+    std::vector<uint8_t> decode(std::string_view str, uint8_t base, const char *digits, const int8_t *map) noexcept
+    {
+        std::vector<uint8_t> data(baseN::sizeDecoded(str, base));
+        baseN::decode(str.data(), str.size(), data.data(), data.size(), base, digits, map);
+        data.erase(data.begin(), std::find_if(data.begin(), data.end(), [](uint8_t item)
+                                              { return item != 0; }));
+        return data;
+    }
 }
\ No newline at end of file
diff --git a/test/test-baseN.cpp b/test/test-baseN.cpp
index a53e824..d895d9b 100644
--- a/test/test-baseN.cpp
+++ b/test/test-baseN.cpp
@@ -47,19 +47,20 @@ TEST(baseN, encode_1e3)
     std::fill(data.begin(), data.end(), 1);
     encode(data, 58, b58digits);
 }
-// TEST(baseN, decode)
-// {
-//     EXPECT_EQ(hex::encode(decode("Ky", 58, b58digits, b58map)), "044c");
-//     EXPECT_EQ(hex::encode(decode("KyK", 58, b58digits, b58map)), "f94a");
-//     EXPECT_EQ(hex::encode(decode("KyKX", 58, b58digits, b58map)), "387ae2");
-//     EXPECT_EQ(hex::encode(decode("KyKXa", 58, b58digits, b58map)), "0ccbd755");
-//     EXPECT_EQ(hex::encode(decode("KyKXaa", 58, b58digits, b58map)), "02e62ec963");
-// }
-// TEST(baseN, decode_1e4)
-// {
-//     std::string str(1e4, '1');
-//     decode(str, 58, b58digits, b58map, str.size() * 733 / 1000 + 1);
-// }
+TEST(baseN, decode)
+{
+    EXPECT_EQ(hex::encode(decode("", 58, b58digits, b58map)), "");
+    EXPECT_EQ(hex::encode(decode("Ky", 58, b58digits, b58map)), "044c");
+    EXPECT_EQ(hex::encode(decode("KyK", 58, b58digits, b58map)), "f94a");
+    EXPECT_EQ(hex::encode(decode("KyKX", 58, b58digits, b58map)), "387ae2");
+    EXPECT_EQ(hex::encode(decode("KyKXa", 58, b58digits, b58map)), "0ccbd755");
+    EXPECT_EQ(hex::encode(decode("KyKXaa", 58, b58digits, b58map)), "02e62ec963");
+}
+TEST(baseN, decode_1e3)
+{
+    std::string str(1e3, '2');
+    decode(str, 58, b58digits, b58map);
+}
 
 int main(int argc, char **argv)
 {