Simplify FindNextFixedWidth

Desbordante · Jan 6, 2025 · 1bd7606 · 1bd7606
1 parent 42d9266
commit 1bd7606
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Showing 2 changed files with 7 additions and 13 deletions.
diff --git a/src/core/util/bitset_extensions.cpp b/src/core/util/bitset_extensions.cpp
@@ -32,20 +32,11 @@ size_t FindNextFixedWidth(std::bitset<kWidth> const& bs, size_t pos) {
     size_t bit_pos = pos % 8ul;
     for (size_t byte_idx{start_byte}; byte_idx < kNumBytes; ++byte_idx) {
         auto byte = GetByte(val, byte_idx);
+        if (byte_idx == start_byte) {
+            byte &= kFirstBits[bit_pos];
+        }
         if (byte > 0ul) {
-            if (byte_idx > start_byte) {
-                return byte_idx * 8ul + std::countr_zero(byte);
-            } else {
-                size_t leading_zeros = std::countl_zero(byte);
-                if (leading_zeros < 7ul - bit_pos) {
-                    std::bitset<8> bs{byte};
-                    for (size_t i{bit_pos + 1}; i < 8ul; ++i) {
-                        if (bs[i]) {
-                            return start_byte * 8ul + i;
-                        }
-                    }
-                }
-            }
+            return byte_idx * 8ul + std::countr_zero(byte);
         }
     }
     return kWidth;

diff --git a/src/core/util/bitset_extensions.h b/src/core/util/bitset_extensions.h
@@ -23,6 +23,9 @@ static std::vector<unsigned long long> const kBytes{
         0x00'00'00'00'00'00'00'ff, 0x00'00'00'00'00'00'ff'00, 0x00'00'00'00'ff'ff'00'00,
         0x00'00'00'00'ff'00'00'00, 0x00'00'00'ff'00'00'00'00, 0x00'00'ff'00'00'00'00'00,
         0x00'ff'00'00'00'00'00'00, 0xff'00'00'00'00'00'00'00};
+static std::vector<unsigned char> const kFirstBits {
+    0b11111110, 0b11111100, 0b11111000, 0b11110000, 0b11100000, 0b11000000, 0b10000000, 0b00000000
+};
 constexpr static size_t kNumBytes = 8;
 constexpr static size_t kWidth = 64;