  Polar codes can be decoded with the low-complexity successive-cancellation
flip (SCF) algorithm. To improve error-correction performance, the dynamic
successive-cancellation flip (DSCF) variant was proposed, where the resulting
error-correction performance is similar to that of the successive-cancellation
list algorithm with low to moderate list sizes. Regardless of the variant, the
SCF algorithm exhibits a variable execution time with a high (worst-case)
latency. In this work, we propose an early-stopping metric used to detect
codewords that are likely undecodable such that the decoder can be stopped at
earlier stages for those codewords. We then propose a modified version of the
DSCF algorithm that integrates our early-stopping metric that exploits the
specific properties of DSCF. Compared to the original DSCF algorithm, in the
region of interest for wireless communications, simulation results show that
our proposed modifications can lead to reductions of 22% to the average
execution time and of 45% to the execution-time variance at the cost of a minor
error-correction loss of approximately 0.05 dB.
