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Forum Index : Microcontroller and PC projects : MM2: Sorting fast with a CFunction
| Author | Message | ||||
| matherp Guru  Joined: 11/12/2012 Location: United KingdomPosts: 10195 |
Inspired by factus10's thread I decided to create a simple cFunction sort which hopefully is generally useful. I'm using a shell sort - code cribbed from rosettacode.org The test script uses the large font table to create a test set of 1020 integers including negative numbers and 255 duplicates. The cFunction returns in about 10msecs with a perfectly sorted result. NOTE this code only runs correctly with firmware version 4.6A In version 4.6 the sort works correctly but the test incorrectly reports errors as there is a bug in 4.6 relating to comparing integers > 30-bits long option default integer option explicit dim integer test(1019) dim integer i,j,l,k=peek(cfunaddr font) for i=0 to 254 ' use test(i)=peek(word k+I*8)+(peek(word k+4+I*8)<<32) test(i+255)=peek(word k+I*8)+(peek(word k+4+I*8)<<32)+2 test(i+510)=peek(word k+I*8)+(peek(word k+4+I*8)<<32)+2 'create lots of duplicates test(i+765)= -(peek(word k+I*8)+(peek(word k+4+I*8)<<32)) 'create negative numbers next i timer=0 j=shellsort(test(),1020) print "Time taken=",timer," msec" j=&H8000000000000000 'maximum negative number possible l=&H7FFFFFFFFFFFFFFF 'maximum positive number possible test(512)=l ' create a spurious error for i=0 to 1019 if test(i)<j then if j=l then print "Test error found", test(i),"<",j else print "ERROR!!!!!!!!!!!!", test(i),"<",j endif endif j=test(i) next i 'long long shellsort (long long a[], long long *nn) { ' long h, l, j, n=*nn; ' long long k; ' for (h = n; h /= 2;) { ' for (l = h; l < n; l++) { ' k = a  ;
' for (j = l; j >= h && k < a[j - h]; j -= h) { ' a[j] = a[j - h]; ' } ' a[j] = k; ' } ' } ' return 0; '} CFunction shellsort 00000000 27bdfff8 afb10004 afb00000 8cad0000 10000032 01a01021 8df10000 8dea0004 01c2282a 14a00022 01c01821 03201821 8f060004 0146282a 14a00005 8f080000 14ca001a 0228282b 50a00019 01c01821 02002821 10000003 01c03821 00603821 01201821 000738c0 00873821 ace80000 ace60004 0062302a 14c0000d 006b4821 8ca80000 8ca60004 0146382a 14e0fff3 00ac2821 14ca0006 0228382b 14e0fff0 00603821 10000003 000318c0 01c01821 000318c0 00831821 ac710000 ac6a0004 25ce0001 27390001 25ef0008 27180008 01cd182a 1460ffd0 26100008 00021fc2 00621021 00021043 1040000e 004d182a 1060fffb 00021fc2 000278c0 008f7821 0080c021 00028023 001080c0 02006021 00908021 00407021 0000c821 1000ffbe 00025823 00001021 00001821 8fb10004 8fb00000 03e00008 27bd0008 End CFunction ' CFunction font 00000000 00000000 00000000 4f5b3e00 00003e5b 4f6b3e00 00003e6b 7c3e1c00 00001c3e 7e3c1800 0000183c 7d571c00 00001c57 7f5e1c00 00001c5e 3c180000 00000018 c3e7ff00 0000ffe7 24180000 00000018 dbe7ff00 0000ffe7 3a060e00 00003048 79292600 00002629 05050700 0000407f 05253f00 0000407f e73c5a00 00005a3c 1c1c0800 00007f3e 1c3e7f00 0000081c 7f221400 00001422 005f5f00 00005f5f 7f017f00 00000609 89956a00 00000066 60606000 00006060 ffa29400 000094a2 7e040800 00000804 7e201000 00001020 2a1c0800 00000808 2a080800 0000081c 10101000 00001e10 0c1e0c00 00000c1e 3e383000 00003038 3e0e0600 0000060e 00000000 00000000 5f000000 00000000 00070000 00000007 147f1400 0000147f 7f2a1200 0000242a 08646200 00002313 56205000 00003649 07030000 00000008 22410000 0000001c 221c0000 00000041 7f1c2a00 00002a1c 3e080800 00000808 70300000 00000080 08080800 00000808 60600000 00000000 08040200 00002010 49453e00 00003e51 7f400000 00000042 49494600 00007249 494d3300 00002141 127f1000 00001814 45453900 00002745 49493100 00003c4a 11090700 00004121 49493600 00003649 49291e00 00004649 14000000 00000000 34000000 00000040 14224100 00000008 14141400 00001414 22140800 00000041 59090600 00000201 5d594e00 00003e41 11127c00 00007c12 49493600 00007f49 41412200 00003e41 41413e00 00007f41 49494100 00007f49 09090100 00007f09 41517300 00003e41 08087f00 00007f08 7f410000 00000041 413f0100 00002040 14224100 00007f08 40404000 00007f40 1c027f00 00007f02 08107f00 00007f04 41413e00 00003e41 09090600 00007f09 51215e00 00003e41 19294600 00007f09 49493200 00002649 7f010300 00000301 40403f00 00003f40 40201f00 00001f20 38403f00 00003f40 08146300 00006314 78040300 00000304 494d4300 00006159 41414100 0000007f 08102000 00000204 41417f00 00000041 01020400 00000402 40404000 00004040 07080000 00000003 54784000 00002054 44443800 00007f28 44442800 00003844 44287f00 00003844 54541800 00003854 7e090200 00000008 a49c7800 000018a4 04047800 00007f08 7d400000 00000044 403d0000 00002040 28440000 00007f10 7f400000 00000041 78047800 00007c04 04047800 00007c08 44443800 00003844 24241800 0000fc18 2418fc00 00001824 04040800 00007c08 54542400 00004854 3f442400 00000404 40207c00 00003c40 40201c00 00001c20 30403c00 00003c40 10284400 00004428 90907c00 00004c90 544c4400 00004464 36410000 00000008 77000000 00000000 36080000 00000041 02040200 00000201 23263c00 00003c26 a1611200 00001ea1 40207a00 00003a40 54555900 00003854 55794100 00002155 54784200 00002254 54784000 00002155 55794000 00002054 52721200 00000c1e 55555900 00003955 54545900 00003954 54545800 00003955 457c4100 00000000 457d4200 00000002 457c4000 00000001 11127d00 00007d12 2528f000 0000f028 55450000 00007c54 547c5400 00002054 097f4900 00007c0a 49493200 00003249 44443a00 00003a44 48483000 0000324a 41217a00 00003a41 40207800 00003a42 a0a07d00 0000009d 42423d00 00003d42 40403d00 00003d40 ff242400 00003c24 49436600 0000487e fc2f2b00 00002b2f 29f62000 0000ff09 7e090300 0000c088 54794100 00002054 447d4100 00000000 484a3200 00003048 40227a00 00003840 0a0a7200 0000007a 19317d00 00007d0d 292f2800 00002629 29292600 00002629 4d402000 00003048 08080800 00003808 08083800 00000808 c8acba00 00002f10 2834fa00 00002f10 7b000000 00000000 2a142200 00000814 2a140800 00002214 5500aa00 0000aa00 aa55aa00 0000aa55 00ff0000 00000000 10ff0000 00001010 14ff0000 00001414 ff00ff00 00001010 f010f000 00001010 14fc0000 00001414 f700ff00 00001414 ff00ff00 00000000 f404fc00 00001414 17101f00 00001414 1f101f00 00001010 141f0000 00001414 10f00000 00001010 001f1000 00000000 101f1000 00001010 10f01000 00001010 00ff1000 00000000 10101000 00001010 10ff1000 00001010 00ff1400 00000000 ff00ff00 00000000 1f101700 00000000 fc04f400 00000000 17101700 00001414 f404f400 00001414 ff00f700 00000000 14141400 00001414 f700f700 00001414 14171400 00001414 1f101f00 00001010 14f41400 00001414 f010f000 00001010 1f101f00 00000000 001f1400 00000000 00fc1400 00000000 f010f000 00000000 ff10ff00 00001010 14ff1400 00001414 101f0000 00001010 00f01000 00000000 ffffff00 0000ffff f0f0f000 0000f0f0 ff000000 0000ffff 00ffff00 00000000 0f0f0f00 00000f0f 44384400 00003844 4a4a3400 0000fc4a 02060600 00007e02 027e0200 0000027e 49416300 00006355 443c0400 00003844 201e2000 0000407e 7e020200 00000602 e7a59900 000099a5 492a1c00 00001c2a 01724c00 00004c72 4d4d3000 0000304a 78483000 00003048 5a463d00 0000bc62 49490000 00003e49 01017e00 00007e01 2a2a2a00 00002a2a 5f444400 00004444 4a444000 00004051 4a514000 00004044 ff010300 00000000 ff000000 0000e080 6b6b0800 00000808 36243600 00003612 090f0600 0000060f 18180000 00000000 10100000 00000000 ff010100 00003040 01011e00 0000001f 1d171200 00000019 3c3c3c00 0000003c 00000000 00000000 End CFunction |
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atmega8 Guru Joined: 19/11/2013 Location: GermanyPosts: 724 |
Hi, i miss the Ccode;-).. THX |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10195 |
In the comments |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3282 |
That is brilliant. Do you mind if I add it to the standard Micromite distribution zip? Geoff Geoff Graham - http://geoffg.net |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10195 |
Of course, no problem |
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| factus10 Regular Member  Joined: 30/12/2014 Location: United StatesPosts: 45 |
Very nice! You might want to give the comb sort a go too. I used code from rosettacode for the version I implemented in 4.5 David |
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| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3282 |
Have you thought of a string sort? That would be useful also. Geoff Geoff Graham - http://geoffg.net |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10195 |
What does it do? |
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twofingers Guru Joined: 02/06/2014 Location: GermanyPosts: 1568 |
Good job! 
sorting strings (sequences of characters)? 
IMHO comb sort seems to be more efficient than shell sort. Regards Michael causality ≠ correlation ≠ coincidence |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10195 |
11msec for comb, 10 for shell, but presumably data dependent. Still unsure of the objective of string sort, do you want to know "fred" is greater than "bert" or sort the letters inside a string? Is "small" bigger then "smaller"? What is it for? I need a proper spec 
option default integer option explicit dim integer test(1019) dim integer i,j,l,k=peek(cfunaddr font) for i=0 to 254 ' use test(i)=peek(word k+I*8)+(peek(word k+4+I*8)<<32) test(i+255)=peek(word k+I*8)+(peek(word k+4+I*8)<<32)+2 test(i+510)=peek(word k+I*8)+(peek(word k+4+I*8)<<32)+2 'create lots of duplicates test(i+765)= -(peek(word k+I*8)+(peek(word k+4+I*8)<<32)) 'create negative numbers next i timer=0 j=shellsort(test(),1020) print "Time taken=",timer," msec" j=&H8000000000000000 'maximum negative number possible l=&H7FFFFFFFFFFFFFFF 'maximum positive number possible test(512)=l ' create a spurious error for i=0 to 1019 if test(i)<j then if j=l then print "Test error found", test(i),"<",j else print "ERROR!!!!!!!!!!!!", test(i),"<",j endif endif j=test(i) next i for i=0 to 254 ' use test(i)=peek(word k+I*8)+(peek(word k+4+I*8)<<32) test(i+255)=peek(word k+I*8)+(peek(word k+4+I*8)<<32)+2 test(i+510)=peek(word k+I*8)+(peek(word k+4+I*8)<<32)+2 'create lots of duplicates test(i+765)= -(peek(word k+I*8)+(peek(word k+4+I*8)<<32)) 'create negative numbers next i timer=0 j=Combsort11(test(),1020) print "Time taken=",timer," msec" j=&H8000000000000000 'maximum negative number possible l=&H7FFFFFFFFFFFFFFF 'maximum positive number possible test(512)=l ' create a spurious error for i=0 to 1019 if test(i)<j then if j=l then print "Test error found", test(i),"<",j else print "ERROR!!!!!!!!!!!!", test(i),"<",j endif endif j=test(i) next i end 'long long combsort(long long a[], long long *nn) '{ ' long l, j, gap, swapped = 1,nElements=*nn; ' long long temp; ' ' gap = nElements; ' while (gap > 1 || swapped == 1) ' { ' gap = gap * 10 / 13; ' if (gap == 9 || gap == 10) gap = 11; ' if (gap < 1) gap = 1; ' swapped = 0; ' for (l = 0, j = gap; j < nElements; l++, j++) ' { ' if (a > a[j])
' { ' temp = a ;
' a = a[j];
' a[j] = temp; ' swapped = 1; ' } ' } ' } '} 'long long shellsort (long long a[], long long *nn) { ' long h, l, j, n=*nn; ' long long k; ' for (h = n; h /= 2;) { ' for (l = h; l < n; l++) { ' k = a ;
' for (j = l; j >= h && k < a[j - h]; j -= h) { ' a[j] = a[j - h]; ' } ' a[j] = k; ' } ' } ' return 0; '} CFunction combsort 00000000 8ca30000 00603821 24080001 24050001 1000002c 2402000d 000738c0 00c73021 00c2001a 004001f4 00004012 2508fff7 2d080002 15000004 00003812 0007302a 10000002 00a6380a 2407000b 00e3302a 10c0001c 00004021 00804821 000730c0 00863021 00e05021 01207021 8d380000 8d2b0004 00c06821 8ccc0004 018b782a 15e00006 8cd90000 556c000a 254a0001 0338782b 51e00007 254a0001 add90000 adcc0004 adb80000 adab0004 00a04021 254a0001 25290008 0143582a 1560ffea 24c60008 28e60002 10c0ffd3 00073040 1105ffd2 000738c0 03e00008 00000000 End CFunction ' CFunction shellsort 00000000 27bdfff8 afb10004 afb00000 8cad0000 10000032 01a01021 8df10000 8dea0004 01c2282a 14a00022 01c01821 03201821 8f060004 0146282a 14a00005 8f080000 14ca001a 0228282b 50a00019 01c01821 02002821 10000003 01c03821 00603821 01201821 000738c0 00873821 ace80000 ace60004 0062302a 14c0000d 006b4821 8ca80000 8ca60004 0146382a 14e0fff3 00ac2821 14ca0006 0228382b 14e0fff0 00603821 10000003 000318c0 01c01821 000318c0 00831821 ac710000 ac6a0004 25ce0001 27390001 25ef0008 27180008 01cd182a 1460ffd0 26100008 00021fc2 00621021 00021043 1040000e 004d182a 1060fffb 00021fc2 000278c0 008f7821 0080c021 00028023 001080c0 02006021 00908021 00407021 0000c821 1000ffbe 00025823 00001021 00001821 8fb10004 8fb00000 03e00008 27bd0008 End CFunction ' CFunction font 00000000 00000000 00000000 4f5b3e00 00003e5b 4f6b3e00 00003e6b 7c3e1c00 00001c3e 7e3c1800 0000183c 7d571c00 00001c57 7f5e1c00 00001c5e 3c180000 00000018 c3e7ff00 0000ffe7 24180000 00000018 dbe7ff00 0000ffe7 3a060e00 00003048 79292600 00002629 05050700 0000407f 05253f00 0000407f e73c5a00 00005a3c 1c1c0800 00007f3e 1c3e7f00 0000081c 7f221400 00001422 005f5f00 00005f5f 7f017f00 00000609 89956a00 00000066 60606000 00006060 ffa29400 000094a2 7e040800 00000804 7e201000 00001020 2a1c0800 00000808 2a080800 0000081c 10101000 00001e10 0c1e0c00 00000c1e 3e383000 00003038 3e0e0600 0000060e 00000000 00000000 5f000000 00000000 00070000 00000007 147f1400 0000147f 7f2a1200 0000242a 08646200 00002313 56205000 00003649 07030000 00000008 22410000 0000001c 221c0000 00000041 7f1c2a00 00002a1c 3e080800 00000808 70300000 00000080 08080800 00000808 60600000 00000000 08040200 00002010 49453e00 00003e51 7f400000 00000042 49494600 00007249 494d3300 00002141 127f1000 00001814 45453900 00002745 49493100 00003c4a 11090700 00004121 49493600 00003649 49291e00 00004649 14000000 00000000 34000000 00000040 14224100 00000008 14141400 00001414 22140800 00000041 59090600 00000201 5d594e00 00003e41 11127c00 00007c12 49493600 00007f49 41412200 00003e41 41413e00 00007f41 49494100 00007f49 09090100 00007f09 41517300 00003e41 08087f00 00007f08 7f410000 00000041 413f0100 00002040 14224100 00007f08 40404000 00007f40 1c027f00 00007f02 08107f00 00007f04 41413e00 00003e41 09090600 00007f09 51215e00 00003e41 19294600 00007f09 49493200 00002649 7f010300 00000301 40403f00 00003f40 40201f00 00001f20 38403f00 00003f40 08146300 00006314 78040300 00000304 494d4300 00006159 41414100 0000007f 08102000 00000204 41417f00 00000041 01020400 00000402 40404000 00004040 07080000 00000003 54784000 00002054 44443800 00007f28 44442800 00003844 44287f00 00003844 54541800 00003854 7e090200 00000008 a49c7800 000018a4 04047800 00007f08 7d400000 00000044 403d0000 00002040 28440000 00007f10 7f400000 00000041 78047800 00007c04 04047800 00007c08 44443800 00003844 24241800 0000fc18 2418fc00 00001824 04040800 00007c08 54542400 00004854 3f442400 00000404 40207c00 00003c40 40201c00 00001c20 30403c00 00003c40 10284400 00004428 90907c00 00004c90 544c4400 00004464 36410000 00000008 77000000 00000000 36080000 00000041 02040200 00000201 23263c00 00003c26 a1611200 00001ea1 40207a00 00003a40 54555900 00003854 55794100 00002155 54784200 00002254 54784000 00002155 55794000 00002054 52721200 00000c1e 55555900 00003955 54545900 00003954 54545800 00003955 457c4100 00000000 457d4200 00000002 457c4000 00000001 11127d00 00007d12 2528f000 0000f028 55450000 00007c54 547c5400 00002054 097f4900 00007c0a 49493200 00003249 44443a00 00003a44 48483000 0000324a 41217a00 00003a41 40207800 00003a42 a0a07d00 0000009d 42423d00 00003d42 40403d00 00003d40 ff242400 00003c24 49436600 0000487e fc2f2b00 00002b2f 29f62000 0000ff09 7e090300 0000c088 54794100 00002054 447d4100 00000000 484a3200 00003048 40227a00 00003840 0a0a7200 0000007a 19317d00 00007d0d 292f2800 00002629 29292600 00002629 4d402000 00003048 08080800 00003808 08083800 00000808 c8acba00 00002f10 2834fa00 00002f10 7b000000 00000000 2a142200 00000814 2a140800 00002214 5500aa00 0000aa00 aa55aa00 0000aa55 00ff0000 00000000 10ff0000 00001010 14ff0000 00001414 ff00ff00 00001010 f010f000 00001010 14fc0000 00001414 f700ff00 00001414 ff00ff00 00000000 f404fc00 00001414 17101f00 00001414 1f101f00 00001010 141f0000 00001414 10f00000 00001010 001f1000 00000000 101f1000 00001010 10f01000 00001010 00ff1000 00000000 10101000 00001010 10ff1000 00001010 00ff1400 00000000 ff00ff00 00000000 1f101700 00000000 fc04f400 00000000 17101700 00001414 f404f400 00001414 ff00f700 00000000 14141400 00001414 f700f700 00001414 14171400 00001414 1f101f00 00001010 14f41400 00001414 f010f000 00001010 1f101f00 00000000 001f1400 00000000 00fc1400 00000000 f010f000 00000000 ff10ff00 00001010 14ff1400 00001414 101f0000 00001010 00f01000 00000000 ffffff00 0000ffff f0f0f000 0000f0f0 ff000000 0000ffff 00ffff00 00000000 0f0f0f00 00000f0f 44384400 00003844 4a4a3400 0000fc4a 02060600 00007e02 027e0200 0000027e 49416300 00006355 443c0400 00003844 201e2000 0000407e 7e020200 00000602 e7a59900 000099a5 492a1c00 00001c2a 01724c00 00004c72 4d4d3000 0000304a 78483000 00003048 5a463d00 0000bc62 49490000 00003e49 01017e00 00007e01 2a2a2a00 00002a2a 5f444400 00004444 4a444000 00004051 4a514000 00004044 ff010300 00000000 ff000000 0000e080 6b6b0800 00000808 36243600 00003612 090f0600 0000060f 18180000 00000000 10100000 00000000 ff010100 00003040 01011e00 0000001f 1d171200 00000019 3c3c3c00 0000003c 00000000 00000000 End CFunction |
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| factus10 Regular Member Joined: 30/12/2014 Location: United StatesPosts: 45 |
Most folks want to be able to sort an array of strings, to put the items in the array in alpha (or inverse) order. |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10195 |
Hi factus10 Still too many unknowns to code anything useful. What about upper and lower case? Sorting on ASCII code is easy but is it useful? And the string length question is still unclear.  |
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| factus10 Regular Member Joined: 30/12/2014 Location: United StatesPosts: 45 |
Yep, true, lots of unknowns. In my code, I changed the comparisons from numeric values to string values. I also added an option to make the string comparisons case insensitive. That's probably good enough for most folks. I can definitely understand the desire to solve the problem once :) Best, David |
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| twofingers Guru Joined: 02/06/2014 Location: GermanyPosts: 1568 |
@Peter That was fast! Cool!
I think the first thing we need is sorting on ASCII code. (MMBasic: "peter" > "Peter") Yes! But it is not the universal solution. The shorter strings should be first. (MMBasic: "Peter" is smaller than "Peters") As in our telephone directory. Regards Michael causality ≠ correlation ≠ coincidence |
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| factus10 Regular Member Joined: 30/12/2014 Location: United StatesPosts: 45 |
A simple comparison (strcmp(string1,string2)) will address string length. Here's an example: http://www.tutorialspoint.com/ansi_c/c_strcmp.htm |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
And I think numerics come before alphas and non-alphanumerics come before numbers, like directory listings: ##@-- . .. ... ..00123456 ..123456 0012346 01 Puff the magic dragon Puff the magic dragon Puff the #1 magic dragon etc? Greg |
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| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3282 |
Sorry, I have been away while this discussion continued and I should have been more specific in the first place. I was thinking of sorting an array of strings. As it would be similar to a numeric sort it should be easy to do and would be another useful tool. Once you have a sorted array of strings you can do high speed binary searches, etc. The syntax could be something like: r = StringSort( ArrayOfStrings(), NbrOfStrings, MaxLengthOfString ) MMBasic stores arrays of strings in a similar fashion as arrays of integers and the CFunction would receive a pointer to the first byte of the first string in the array. The space allocated to each string defaults to 255 bytes but this can be changed with the LENGTH parameter in the DIM command. This is why I suggested the MaxLengthOfString parameter so that this info can be passed. Each string comes straight after the preceeding so you can step through the array using: ptr = ptr + MaxLengthOfString
In MMBasic the actual length of the string is stored in the first byte and can range from zero to MaxLengthOfString. The 2nd, 3rd, etc bytes store the characters of the string. Most string sorts treat upper case and lower case as different and I think that this would be sufficient. However, if you wanted to go overboard you could have a fourth parameter to the CFunction that would specify a case independent sort. Geoff Geoff Graham - http://geoffg.net |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10195 |
Geoff If I have a string s$= "fred" length 10, can I assume anything about the contents of the 6 unused bytes or are these just going to contain whatever. So if I then go s$="fr" do the 3rd and 4th bytes stay as "ed" and just the length get changed? Peter |
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| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3282 |
No, you cannot assume anything about the unused bytes, they contain junk. As you said the 3rd and 4th bytes would hold whatever was left over from the previous contents but this is not guaranteed. So, when you compare strings you must take into account the length stored in the first byte. This is the code used in the MMBasic source: // compare two MMBasic style strings // returns 1 if s1 > s2 or 0 if s1 = s2 or -1 if s1 < s2 int Mstrcmp(unsigned char *s1, unsigned char *s2) { register int i; register unsigned char *p1, *p2; // get the smaller length i = *s1 < *s2 ? *s1 : *s2; // skip the length byte and point to the char array p1 = s1 + 1; p2 = s2 + 1; // compare each char while(i--) { if(*p1 > *p2) return 1; if(*p1 < *p2) return -1; p1++; p2++; } // up to this point the strings matched // make the decision based on which one is shorter if(*s1 > *s2) return 1; if(*s1 < *s2) return -1; return 0; } Geoff Geoff Graham - http://geoffg.net |
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