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About “diff -dâ€
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The diff implementation on OpenBSD has a non-standard -d option with the following documentation:
-d
Try very hard to produce a diff as small as possible. This may
consume a lot of processing power and memory when processing
large files with many changes.
The GNU diff implementation has the same option with the shorter documentation
-d,--minimal
try hard to find a smaller set of changes
From time to time I've used this option just to see if it generates output that is in any shape or form different from the same diff command without the option, bit I've never seen any difference (no pun intended).
Could someone provide or point to an example where this option actually produces a different result from the same command without -d? Alternatively, if someone could explain the circumstances required for this option to kick in. I'm also uncertain whether "minimal" means "fewer lines of output" or "fewer hunks".
An uneducated guess is that it has to do with very large hunks.
diff
asked 2 hours ago
Kusalananda
107k14209331
add a comment |Â
up vote
5
down vote
favorite
The diff implementation on OpenBSD has a non-standard -d option with the following documentation:
-d
Try very hard to produce a diff as small as possible. This may
consume a lot of processing power and memory when processing
large files with many changes.
The GNU diff implementation has the same option with the shorter documentation
-d,--minimal
try hard to find a smaller set of changes
From time to time I've used this option just to see if it generates output that is in any shape or form different from the same diff command without the option, bit I've never seen any difference (no pun intended).
Could someone provide or point to an example where this option actually produces a different result from the same command without -d? Alternatively, if someone could explain the circumstances required for this option to kick in. I'm also uncertain whether "minimal" means "fewer lines of output" or "fewer hunks".
An uneducated guess is that it has to do with very large hunks.
diff
asked 2 hours ago
Kusalananda
107k14209331
unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
– JdeBP
1 hour ago
@JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
– Kusalananda
1 hour ago
info diff performanceexplains it IIRC
– Stéphane Chazelas
1 hour ago
add a comment |Â
up vote
5
down vote
favorite
up vote
5
down vote
favorite
The diff implementation on OpenBSD has a non-standard -d option with the following documentation:
-d
Try very hard to produce a diff as small as possible. This may
consume a lot of processing power and memory when processing
large files with many changes.
The GNU diff implementation has the same option with the shorter documentation
-d,--minimal
try hard to find a smaller set of changes
From time to time I've used this option just to see if it generates output that is in any shape or form different from the same diff command without the option, bit I've never seen any difference (no pun intended).
Could someone provide or point to an example where this option actually produces a different result from the same command without -d? Alternatively, if someone could explain the circumstances required for this option to kick in. I'm also uncertain whether "minimal" means "fewer lines of output" or "fewer hunks".
An uneducated guess is that it has to do with very large hunks.
diff
asked 2 hours ago
Kusalananda
107k14209331
The diff implementation on OpenBSD has a non-standard -d option with the following documentation:
-d
Try very hard to produce a diff as small as possible. This may
consume a lot of processing power and memory when processing
large files with many changes.
The GNU diff implementation has the same option with the shorter documentation
-d,--minimal
try hard to find a smaller set of changes
From time to time I've used this option just to see if it generates output that is in any shape or form different from the same diff command without the option, bit I've never seen any difference (no pun intended).
Could someone provide or point to an example where this option actually produces a different result from the same command without -d? Alternatively, if someone could explain the circumstances required for this option to kick in. I'm also uncertain whether "minimal" means "fewer lines of output" or "fewer hunks".
An uneducated guess is that it has to do with very large hunks.
diff
diff
asked 2 hours ago
Kusalananda
107k14209331
asked 2 hours ago
Kusalananda
107k14209331
edited 1 hour ago
asked 2 hours ago
Kusalananda
107k14209331
asked 2 hours ago
Kusalananda
107k14209331
asked 2 hours ago
Kusalananda
107k14209331
107k14209331
unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
– JdeBP
1 hour ago
@JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
– Kusalananda
1 hour ago
info diff performanceexplains it IIRC
– Stéphane Chazelas
1 hour ago
add a comment |Â
unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
– JdeBP
1 hour ago
@JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
– Kusalananda
1 hour ago
info diff performanceexplains it IIRC
– Stéphane Chazelas
1 hour ago
unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
– JdeBP
1 hour ago
unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
– JdeBP
1 hour ago
@JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
– Kusalananda
1 hour ago
@JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
– Kusalananda
1 hour ago
info diff performance explains it IIRC– Stéphane Chazelas
1 hour ago
info diff performance explains it IIRC– Stéphane Chazelas
1 hour ago
add a comment |Â
1 Answer
1
active
oldest
votes
up vote
3
down vote
In GNU diff, also used on FreeBSD, the --minimal flag triggers an algorithm variation by Paul Eggert that causes it "to limit the cost to O(N**1.5 log N) at the price of producing suboptimal output for large inputs with differences". More specifically, it causes it to not apply several heuristics that deal in finding merely close to optimal solutions and in throwing out "confusing" lines as extra differences.
In OpenBSD diff, which uses the older Unix diff algorithm from the 1970s, the algorithm employed is credited to Harold Stone, and the --minimal flag triggers a search that is (effectively un-) bounded by the maximum value of an unsigned integer instead of by the square root of the size of the range of lines being compared (or 256 if it is greater).
Further reading
- Eugene W. Myers (November 1986). "An O(ND) difference algorithm and its variations". Algorithmica. Volume 1. Issue 1–4. pp. 251–266. DOI 10.1007/BF01840446.
- J. W. Hunt and M. D. McIlroy (June 1976). "An Algorithm for Differential File Comparison". Report 41. Computing Science. Bell Laboratories.
- Richard Hartman (1988-01-13). Unix diff(1) algorithm.
23225@cca.CCA.COM. comp.unix.questions. - https://github.com/openbsd/src/blob/d1e24f318523607c98dc6fbe5a06a5d9e5c87293/usr.bin/diff/diffreg.c#L93
- https://github.com/freebsd/freebsd/blob/40ec4fdc9a74bfdb83f13672acdb88af5c91ab46/contrib/diff/src/analyze.c#L23
edited 39 mins ago
Stephen Kitt
148k22324393
answered 50 mins ago
JdeBP
29.8k461136
When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
– schily
41 mins ago
add a comment |Â
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
In GNU diff, also used on FreeBSD, the --minimal flag triggers an algorithm variation by Paul Eggert that causes it "to limit the cost to O(N**1.5 log N) at the price of producing suboptimal output for large inputs with differences". More specifically, it causes it to not apply several heuristics that deal in finding merely close to optimal solutions and in throwing out "confusing" lines as extra differences.
In OpenBSD diff, which uses the older Unix diff algorithm from the 1970s, the algorithm employed is credited to Harold Stone, and the --minimal flag triggers a search that is (effectively un-) bounded by the maximum value of an unsigned integer instead of by the square root of the size of the range of lines being compared (or 256 if it is greater).
Further reading
- Eugene W. Myers (November 1986). "An O(ND) difference algorithm and its variations". Algorithmica. Volume 1. Issue 1–4. pp. 251–266. DOI 10.1007/BF01840446.
- J. W. Hunt and M. D. McIlroy (June 1976). "An Algorithm for Differential File Comparison". Report 41. Computing Science. Bell Laboratories.
- Richard Hartman (1988-01-13). Unix diff(1) algorithm.
23225@cca.CCA.COM. comp.unix.questions. - https://github.com/openbsd/src/blob/d1e24f318523607c98dc6fbe5a06a5d9e5c87293/usr.bin/diff/diffreg.c#L93
- https://github.com/freebsd/freebsd/blob/40ec4fdc9a74bfdb83f13672acdb88af5c91ab46/contrib/diff/src/analyze.c#L23
edited 39 mins ago
Stephen Kitt
148k22324393
answered 50 mins ago
JdeBP
29.8k461136
When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
– schily
41 mins ago
add a comment |Â
up vote
3
down vote
In GNU diff, also used on FreeBSD, the --minimal flag triggers an algorithm variation by Paul Eggert that causes it "to limit the cost to O(N**1.5 log N) at the price of producing suboptimal output for large inputs with differences". More specifically, it causes it to not apply several heuristics that deal in finding merely close to optimal solutions and in throwing out "confusing" lines as extra differences.
In OpenBSD diff, which uses the older Unix diff algorithm from the 1970s, the algorithm employed is credited to Harold Stone, and the --minimal flag triggers a search that is (effectively un-) bounded by the maximum value of an unsigned integer instead of by the square root of the size of the range of lines being compared (or 256 if it is greater).
Further reading
- Eugene W. Myers (November 1986). "An O(ND) difference algorithm and its variations". Algorithmica. Volume 1. Issue 1–4. pp. 251–266. DOI 10.1007/BF01840446.
- J. W. Hunt and M. D. McIlroy (June 1976). "An Algorithm for Differential File Comparison". Report 41. Computing Science. Bell Laboratories.
- Richard Hartman (1988-01-13). Unix diff(1) algorithm.
23225@cca.CCA.COM. comp.unix.questions. - https://github.com/openbsd/src/blob/d1e24f318523607c98dc6fbe5a06a5d9e5c87293/usr.bin/diff/diffreg.c#L93
- https://github.com/freebsd/freebsd/blob/40ec4fdc9a74bfdb83f13672acdb88af5c91ab46/contrib/diff/src/analyze.c#L23
edited 39 mins ago
Stephen Kitt
148k22324393
answered 50 mins ago
JdeBP
29.8k461136
When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
– schily
41 mins ago
add a comment |Â
up vote
3
down vote
up vote
3
down vote
In GNU diff, also used on FreeBSD, the --minimal flag triggers an algorithm variation by Paul Eggert that causes it "to limit the cost to O(N**1.5 log N) at the price of producing suboptimal output for large inputs with differences". More specifically, it causes it to not apply several heuristics that deal in finding merely close to optimal solutions and in throwing out "confusing" lines as extra differences.
In OpenBSD diff, which uses the older Unix diff algorithm from the 1970s, the algorithm employed is credited to Harold Stone, and the --minimal flag triggers a search that is (effectively un-) bounded by the maximum value of an unsigned integer instead of by the square root of the size of the range of lines being compared (or 256 if it is greater).
Further reading
- Eugene W. Myers (November 1986). "An O(ND) difference algorithm and its variations". Algorithmica. Volume 1. Issue 1–4. pp. 251–266. DOI 10.1007/BF01840446.
- J. W. Hunt and M. D. McIlroy (June 1976). "An Algorithm for Differential File Comparison". Report 41. Computing Science. Bell Laboratories.
- Richard Hartman (1988-01-13). Unix diff(1) algorithm.
23225@cca.CCA.COM. comp.unix.questions. - https://github.com/openbsd/src/blob/d1e24f318523607c98dc6fbe5a06a5d9e5c87293/usr.bin/diff/diffreg.c#L93
- https://github.com/freebsd/freebsd/blob/40ec4fdc9a74bfdb83f13672acdb88af5c91ab46/contrib/diff/src/analyze.c#L23
edited 39 mins ago
Stephen Kitt
148k22324393
answered 50 mins ago
JdeBP
29.8k461136
In GNU diff, also used on FreeBSD, the --minimal flag triggers an algorithm variation by Paul Eggert that causes it "to limit the cost to O(N**1.5 log N) at the price of producing suboptimal output for large inputs with differences". More specifically, it causes it to not apply several heuristics that deal in finding merely close to optimal solutions and in throwing out "confusing" lines as extra differences.
In OpenBSD diff, which uses the older Unix diff algorithm from the 1970s, the algorithm employed is credited to Harold Stone, and the --minimal flag triggers a search that is (effectively un-) bounded by the maximum value of an unsigned integer instead of by the square root of the size of the range of lines being compared (or 256 if it is greater).
Further reading
- Eugene W. Myers (November 1986). "An O(ND) difference algorithm and its variations". Algorithmica. Volume 1. Issue 1–4. pp. 251–266. DOI 10.1007/BF01840446.
- J. W. Hunt and M. D. McIlroy (June 1976). "An Algorithm for Differential File Comparison". Report 41. Computing Science. Bell Laboratories.
- Richard Hartman (1988-01-13). Unix diff(1) algorithm.
23225@cca.CCA.COM. comp.unix.questions. - https://github.com/openbsd/src/blob/d1e24f318523607c98dc6fbe5a06a5d9e5c87293/usr.bin/diff/diffreg.c#L93
- https://github.com/freebsd/freebsd/blob/40ec4fdc9a74bfdb83f13672acdb88af5c91ab46/contrib/diff/src/analyze.c#L23
edited 39 mins ago
Stephen Kitt
148k22324393
answered 50 mins ago
JdeBP
29.8k461136
edited 39 mins ago
Stephen Kitt
148k22324393
edited 39 mins ago
Stephen Kitt
148k22324393
edited 39 mins ago
Stephen Kitt
148k22324393
148k22324393
answered 50 mins ago
JdeBP
29.8k461136
answered 50 mins ago
JdeBP
29.8k461136
answered 50 mins ago
JdeBP
29.8k461136
29.8k461136
When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
– schily
41 mins ago
add a comment |Â
When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
– schily
41 mins ago
When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
– schily
41 mins ago
When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
– schily
41 mins ago
add a comment |Â
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unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
– JdeBP
1 hour ago
@JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
– Kusalananda
1 hour ago
info diff performanceexplains it IIRC– Stéphane Chazelas
1 hour ago