Possible bug in _raqm_reorder_runs

[deepakjois]

libraqm/src/raqm.c

Line 996 in 3241d49

for (level = max_level; level > 0; level--)

In the code:

for (level = max_level; level > 0; level--)

The spec says:

L2. From the highest level found in the text to the lowest odd level on each line…

The code above seems to assume that the lowest odd level is always 1. I am not sure if it makes any difference in practice. I was reading through the code because I want to reimplement parts of this file in Lua, and this seemed to be not according to my understanding of the spec.

[deepakjois]

A spec-compliant implementation would be to determine minimum level as well as maximum level for the line. Something similar what is done in the BiDi reference implementation (reproduced below in Lua):

From: https://github.com/deepakjois/luabidi/blob/4b90e7acc14a5f3173e7f5eb88fb501bc9c9dca4/src/bidi.lua#L1118

  local highestLevel = 0
  local lowestOddLevel = MAX_DEPTH + 2
  for i = 1, lineLength do
    local level = levels[i]
    if level > highestLevel then highestLevel = level end
    if bit32.band(level, 1) ~= 0 and level < lowestOddLevel then lowestOddLevel = level end
  end

MAX_DEPTH is defined in the standard as 125, so maybe it is available as a constant in the FriBiDi library.