/* * Copyright (c) 1987 Regents of the University of California. * All rights reserved. The Berkeley software License Agreement * specifies the terms and conditions for redistribution. */ #ifdef LIBC_SCCS <@(#)bcmp.s 1.2 (Berkeley) 1/8/87\0> .even #endif LIBC_SCCS #include "DEFS.h" /* * bcmp(b1, b2, length) * * Compare length bytes starting at b1 and b2 - return 0 if equal, non zero * otherwise. Bcmp uses a cost analysis heuristic to determine if it's worth * while to try for a word comparison. If length > N, then try for a word * comparison. Bcmp will fail if N < 3. 8 is a good value for N: * * Algorithm Cost (in instructions) * byte loop 3 * length * word loop overhead [worst case] 12 * word loop 1.5 * length * * N * 3 > 12 + N * 1.5 * N > 8 */ #define N 8. ENTRY(bcmp) mov 6(sp),r0 / if ((r0 = length) == 0) beq 3f / return(length:r0) mov r2,-(sp) / reserve a register for our use mov 6(sp),r2 / r2 = b2 mov 4(sp),r1 / r1 = b1 cmp r0,\$N / if (length > N) bhi 4f / try words 1: cmpb (r1)+,(r2)+ / do if (*b1++ != *b2++) bne 2f / return(length:r0) {length != 0} sob r0,1b / while (--length) 2: mov (sp)+,r2 / return(length:r0) 3: rts pc /* * The length of the comparison justifies trying a word by word comparison. * If b1 and b2 are of the same parity, we can do a word comparison by * handling any leading and trailing odd bytes separately. */ 4: bit \$1,r1 / if (b1&1 != b2&1) beq 5f / do bytes bit \$1,r2 beq 1b / (b1 odd, b2 even - do bytes) cmpb (r1)+,(r2)+ / if (leading odd bytes equal) bne 2b / return(non_zero::r0) dec r0 / else onto word loop br 6f 5: bit \$1,r2 bne 1b / (b1 even, b2 odd - do bytes) 6: mov r0,-(sp) / save trailing byte indicator asr r0 / length >>= 1 (unsigned) bic \$0100000,r0 / (length is now in remaining words to compare) 7: cmp (r1)+,(r2)+ / do if (*(short *)b1++ != *(short *)b2++) bne 9f / return(length:r0) {length != 0} sob r0,7b / while (--length) 8: mov (sp)+,r0 / if (no odd trailing byte) bic \$!1,r0 beq 2b / return(0) cmpb (r1)+,(r2)+ / if (trailing odd bytes different) bne 2b / return(non-zero) clr r0 / else return(0) br 2b 9: mov (sp)+,r0 / bad compare in word loop, br 2b / return(non-zero)