tmin: Proposing del_len option for improved speed

[gnbon]

Issue

Block deletion in the tmin stage is a time-consuming task that scales with the size of the file.

Background

winafl/afl-tmin.c

Lines 911 to 923 in 25d5840

	del_len = next_p2(in_len / TRIM_START_STEPS);
	stage_o_len = in_len;
	ACTF(cBRI "Stage #1: " cRST "Removing blocks of data...");
	next_del_blksize:
	if (!del_len) del_len = 1;
	del_pos = 0;
	prev_del = 1;
	SAYF(cGRA " Block length = %u, remaining size = %u\n" cRST,
	del_len, in_len);

As del_len, the unit for reducing unnecessary blocks, decreases by powers of two, the operation takes longer. However, there are instances
where speed is more critical than achieving minimal minimization.

winafl/afl-tmin.c

Lines 968 to 971 in 25d5840

	if (del_len > 1 && in_len >= 1) {
	del_len /= 2;
	goto next_del_blksize;

Currently, the minimum value of del_len is 1. However, increasing the minimum value would result in faster speeds.

proposal

Therefore, I propose allowing del_len to be specified as an option.

Alternatively, a method could be implemented to terminate the process if there is no reduction of even 1 byte, or if the reduction is less than n bytes, in a given cycle.

[ifratric]

Hi, if this is something you'd like to fix, please go ahead and and submit a pull request.

[gnbon]

Okey. I implemented the feature and submitted the pull request. How does it look?