Hardware interview practice

Count coalesced memory segments

MediumFirmwareC++

A validation model must count the 32-byte memory segments touched by one warp's active four-byte loads. Write the C++ function that returns the number of distinct aligned segments.

Starting point

Question code

int segment_count(const uint32_t addr[32], uint32_t active_mask);

Reviewed example

Work through one case

Input

Activate aligned addresses 0x100, 0x104, and 0x11C in three warp lanes.

Expected output

segment_count returns 1.

Masking each address to a 32-byte base produces the same segment address 0x100.

What to cover

Requirements

Each active lane performs one four-byte load and every active address is four-byte aligned.
A segment is identified by addr[lane] & ~uint32_t(31); count each distinct segment once.
Return zero for active_mask=0; addr may be NULL only in that case, otherwise return -1 for NULL or misalignment.
Use fixed storage only, with no allocation and no reads from inactive lanes.