Under block-aware encoding, a bitmap represented by atoms comprises a series of bitmaps for each data block in a database. Each bitmap in the series is referred to herein as a block bitmap. Each block bitmap may have a different number of bytes or bits. Gaps are represented in atoms using a pair of numbers referred to as a gap code. A gap code includes a block-skip code and slot-skip code. A block-skip code represents how many block bitmaps to advance to reach a subsequent block bitmap; a slot-skip code represents how many bytes to advance within the block bitmap to reach a byte with at least one bit set. A gap code is represented by bit positions within a byte, with some bit positions allocated to represent the block-skip code and some to represent the slot-skip code. The allocation is adjusted dynamically during encoding and decoding.