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| Deletions are marked like this. | Additions are marked like this. |
| Line 8: | Line 8: |
| _:_: then it loops over a set of patches, or iterates on one patch. For each patch it calls | _:_: it loops over a set of patches, or iterates on one patch. For each patch it calls |
| Line 22: | Line 22: |
| loop | _: loop |
| Line 24: | Line 24: |
| for all fno normal[fno] = f (inputs) | _:_: for all fno normal[fno] = f (inputs) |
| Line 26: | Line 26: |
| for a few fno use normal[fno] | _:_: for a few fno use normal[fno] |
| Line 28: | Line 28: |
| change some inputs | _: end loop |
| Line 30: | Line 30: |
| end loop | _: change some inputs |
| Line 32: | Line 32: |
| change some inputs use some normal[fno] |
_: use some normal[fno] |
| Line 40: | Line 38: |
| loop | _: loop |
| Line 42: | Line 40: |
| for all fno __normal[fno].deferred = true__ | _:_: for all fno: normal[fno].deferred = true |
| Line 44: | Line 42: |
| for a few fno __if normal[fno].deferred normal[fno] = f (inputs); normal[fno].deferred = false__ | _:_: for a few fno: use normal[fno], computing it from f (inputs) if is deferred, and changing it to being no-longer deferred |
| Line 46: | Line 44: |
| change some inputs | _: end loop |
| Line 48: | Line 46: |
| end loop | _: compute any remaining deferred normal[fno] before their inputs can change |
| Line 50: | Line 48: |
| __for a few fno if normal[fno].deferred normal[fno] = f (inputs); normal[fno].deferred = false__ | _: change some inputs |
| Line 52: | Line 50: |
| change some inputs | _: use some normal[fno] |
| Line 54: | Line 52: |
| use some normal[fno] |
A variety of techniques have been used.
Deferring calculations until needed
mris_fix_topology has a hot loop, which does unnecessary calculations of the face normals
mrisComputeOptimalRetessellation and mrisComputeRandomRetessellation have a similar structure
_:_: it loops over a set of patches, or iterates on one patch. For each patch it calls
_:_:_: mrisDefectPatchFitness, which calls
_:_:_:_: mrisComputeDefectLogLikelihood, which calls
_:_:_:_:_: mrisComputeDefectMRILogUnlikelihood, which
_:_:_:_:_:_: does an expensive computation all the face normals for ALL the faces
_:_:_:_:_:_: does two other expensive steps, which only use a few of the face normals
To simplify, the original code does this
_: loop
_:_: for all fno normal[fno] = f (inputs)
_:_: for a few fno use normal[fno]
_: end loop
_: change some inputs
_: use some normal[fno]
Since only a few of the face normals are used, it is a waste of time to calculate all of them every time around the loop!
This is replaced by code that does
_: loop
_:_: for all fno: normal[fno].deferred = true
_:_: for a few fno: use normal[fno], computing it from f (inputs) if is deferred, and changing it to being no-longer deferred
_: end loop
_: compute any remaining deferred normal[fno] before their inputs can change
_: change some inputs
_: use some normal[fno]