Module 5 · Decisions
Under the Hood: How a Branch Becomes a Jump
ProReading
Kenji added up the same 32768 numbers 2000 times, first shuffled, then sorted. With GCC's optimiser switched off, the shuffled run took 421 ms and the sorted run 159 ms. Same numbers, same additions, and the sorted order was about 2.6 times faster. Then he compiled the way the Playground does, and the gap disappeared.
Pro lesson
This one goes deeper
It is included with this track and with Learn Pro. Every question on the Skill Test can be answered from the free lessons, so this is depth and never a gate on the certificate.
What is inside Under the Hood: How a Branch Becomes a Jump
- A processor has no if, only jumps
- One if, compiled: a compare and a conditional jump
- The same kind of if with no jump at all: cmov
- A dense switch becomes a jump table
- Branch prediction: the processor guesses
- Kenji's loop, measured
- What this means for you today