Wednesday, August 19

rowhammer

daily challenge16

today's brief

2014. Researchers find that reading the same row of DRAM over and over, fast enough, leaks charge into the rows physically next to it and flips their bits. No bug in any program, just physics winning against density. Someone then turns it into a privilege escalation from JavaScript in a browser tab. The row you hammer is fine. Its neighbours are the ones that change.

Objective

Count the charged cells in the rows immediately above and below the hammered row.

Steps

cells holds h rows of w cells, stored row by row: the cell at row r and column c is cells[r * w + c].
A cell is 1 when it holds charge and 0 when it does not.
Return how many charged cells sit in the row directly above and the row directly below row.
A row at the top or bottom edge only has one neighbour. The hammered row itself never counts.

examples

$ neighbours_at_risk({1,0,0, 0,1,1, 1,1,1, 0,0,1}, 3, 4, 1)

$ neighbours_at_risk({1,0,0, 0,1,1, 1,1,1, 0,0,1}, 3, 4, 0)

$ neighbours_at_risk({1,0,0, 0,1,1, 1,1,1, 0,0,1}, 3, 4, 3)

Constraints

Expected files

dram.c

Allowed functions

None. Write every helper yourself.

Back to compete

Solutions

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