AK: Fix DeprecatedString::bijective_base_from for large numbers

The output of the DeprecatedString::bijective_base_from() is now
correct for numbers larger than base^2.

This makes column names display correctly in Spreadsheet.

1 files changed, 10 insertions, 8 deletions

diff --git a/AK/DeprecatedString.cpp b/AK/DeprecatedString.cpp
index 5877bc7426..437b27a71a 100644
--- a/AK/DeprecatedString.cpp
+++ b/AK/DeprecatedString.cpp
@@ -246,6 +246,7 @@ DeprecatedString DeprecatedString::repeated(StringView string, size_t count)
 
 DeprecatedString DeprecatedString::bijective_base_from(size_t value, unsigned base, StringView map)
 {
+    value++;
     if (map.is_null())
         map = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"sv;
 
@@ -255,15 +256,16 @@ DeprecatedString DeprecatedString::bijective_base_from(size_t value, unsigned ba
     Array<char, round_up_to_power_of_two(sizeof(size_t) * 8 + 1, 2)> buffer;
     size_t i = 0;
     do {
-        buffer[i++] = map[value % base];
-        value /= base;
-    } while (value > 0);
+        auto remainder = value % base;
+        auto new_value = value / base;
+        if (remainder == 0) {
+            new_value--;
+            remainder = map.length();
+        }
 
-    // NOTE: Weird as this may seem, the thing that comes after 'Z' is 'AA', which as a number would be '00'
-    //       to make this work, only the most significant digit has to be in a range of (1..25) as opposed to (0..25),
-    //       but only if it's not the only digit in the string.
-    if (i > 1)
-        --buffer[i - 1];
+        buffer[i++] = map[remainder - 1];
+        value = new_value;
+    } while (value > 0);
 
     for (size_t j = 0; j < i / 2; ++j)
         swap(buffer[j], buffer[i - j - 1]);