all devices regression report - 2017-11-02-15:11:33 - 31cb4cf7aa88784219f6fc2be362a66df2f67289

Differences in all devices errors using gs/examples files

Previous Revision: de651aaa531a7eb6fa99c1ef97682ebe22a3cda7
 Current Revision: 31cb4cf7aa88784219f6fc2be362a66df2f67289

commit 31cb4cf7aa88784219f6fc2be362a66df2f67289
Author:     Robin Watts <[email protected]>
AuthorDate: Fri Oct 27 20:24:32 2017 +0100
CommitDate: Wed Nov 1 13:38:16 2017 +0000

    Tweak cmap functions for speed.
    
    In looking at the Advertising-PowerPoint-A4.pdf file, I noted that
    cmap_gray_direct and cmap_gray_halftoned were taking a noticable
    amount of time. This commit attempts to alleviate that.
    
    Various observations:
    
    1) Avoid unnecessary loop in cmap_gray_halftoned (and similar functions).
    
    In some of the code, we do:
    
     for (i = 0; i < n; i++)
        if (i == k)
           do_something_with(i)
    
    why not just use:
    
      if (k < n)
        do_something_with(k)
    
    2) Typically functions like cmap_gray_direct do a load of work,
    culminating in trying to encode a color value. If that encoding fails,
    it would fallback to trying to use a cmap_gray_halftoned, which would
    do all the work a second time.
    
    Tweak the code to avoid the call, and hence the repetition.
    
    The downside to this is that the work is typically of the form:
    
      for (i = 0; i < n; i++)
        cv[i] = frac2cv(some_calculation_involving(cm_comps[i]));
    
    and in order to be able to avoid the call to cmap_gray_halftoned, we
    need to make it:
    
      for (i = 0; i < n; i++) {
         cm_comps[i] = some_calculation_involving(cm_comps[i]);
         cv[i] = frac2cv(cm_comps[i]);
      }
    
    i.e. we have to do more stores than before. This can hurt us in some
    cases, but it seems like a worthwhile win, especially in light of 3).
    
    3) A lot of the work in these functions involves mapping colors through
    the effective_transfer functions. This happens in code of the form:
    
      for (i = 0; i < n; i++) {
         cm_comps[i] = gx_map_color_frac(pgs, cm_comps[i], effective_transfer[i]);
      }
    
    If effective_transfer[i] is identity (as it almost always is), then
    this whole loop is a nop.
    
    We make some steps to optimise for this case by having the
    gx_map_color_frac macro check for effective_transfer[i] being
    gs_identity_transfer before calling it, but this doesn't help us
    avoid the loop/load/store.
    
    We therefore extend pgs with a count of the number of
    'effective_transfer's that are non identity (essentially a flag
    that enables us to know if we can skip this loop or not),
    and use that to optimise our work.

base/gsht.c
base/gxcmap.c
base/gxgstate.h

new errors:

errors that went away:

errors that are not whitelisted:
=== ghostpdl/examples/transparency_example.ps === cp50 ===
=== ghostpdl/examples/transparency_example.ps === psdrgb ===