Bit Tricks in C

Firmware talks to hardware through registers, which are words where each bit means something. One bit can gate a clock while the next one clears an interrupt. That's why bit questions show up so much in Qualcomm rounds, and why a single-bit operation is a common warm-up, often asked as a C macro. The follow-ups then push on the edges, like a bad bit position or bit 31 on a signed int.

Every problem here uses the same move. You build a mask with shifts, then apply it with AND, OR or XOR. Once that feels routine, the rest is mostly a matter of getting the shift amounts right. The theory behind single-bit work is in Embedded C & OS Internals. Below is the code for each problem, with tests, in six languages.

QualcommPremium lesson · Coding round

The 6 Qualcomm problems are below.

1. 1A Premium questionCoding · Easy · Signature problem
2. 2A Premium questionCoding · Easy · Frequently asked
3. 3A Premium questionCoding · Easy · Frequently asked

+ 3 more in this lesson

Each with hints, the follow-up and a tested solution.

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From 135 Qualcomm reports, forum threads behind logins and write-ups in Chinese.

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