/* * Copyright (c) 2002 Apple Computer, Inc. All rights reserved. * * @APPLE_LICENSE_HEADER_START@ * * Copyright (c) 1999-2003 Apple Computer, Inc. All Rights Reserved. * * This file contains Original Code and/or Modifications of Original Code * as defined in and that are subject to the Apple Public Source License * Version 2.0 (the 'License'). You may not use this file except in * compliance with the License. Please obtain a copy of the License at * http://www.opensource.apple.com/apsl/ and read it before using this * file. * * The Original Code and all software distributed under the License are * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. * Please see the License for the specific language governing rights and * limitations under the License. * * @APPLE_LICENSE_HEADER_END@ */ #define ASSEMBLER #include #undef ASSEMBLER // ***************** // * S T R L C P Y * // ***************** // // size_t strlcpy(char *dst, const char *src, size_t size); // // We optimize the move by doing it word parallel. This introduces // a complication: if we blindly did word load/stores until finding // a 0, we might get a spurious page fault by touching bytes past it. // To avoid this, we never do a "lwz" that crosses a page boundary, // or store unnecessary bytes. // // The test for 0s relies on the following inobvious but very efficient // word-parallel test: // x = dataWord + 0xFEFEFEFF // y = ~dataWord & 0x80808080 // if (x & y) == 0 then no zero found // The test maps any non-zero byte to zero, and any zero byte to 0x80, // with one exception: 0x01 bytes preceeding the first zero are also // mapped to 0x80. .text .globl EXT(strlcpy) .align 5 LEXT(strlcpy) andi. r0,r4,3 // is source aligned? dcbt 0,r4 // touch in source lis r6,hi16(0xFEFEFEFF) // start to load magic constants lis r7,hi16(0x80808080) dcbtst 0,r3 // touch in dst ori r6,r6,lo16(0xFEFEFEFF) ori r7,r7,lo16(0x80808080) mr r9,r3 // use r9 for dest ptr (r3 remembers dst start) beq Laligned // source is aligned subfic r0,r0,4 // r0 <- #bytes to word align source // Copy min(r0,r5) bytes, until 0-byte found. // r0 = #bytes we propose to copy (NOTE: must be >0) // r4 = source ptr (unaligned) // r5 = length remaining in buffer (may be 0) // r6 = 0xFEFEFEFF // r7 = 0x80808080 // r9 = dest ptr (unaligned) Lbyteloop: cmpwi r5,0 // buffer empty? beq-- L0notfound // buffer full but 0 not found lbz r8,0(r4) // r8 <- next source byte subic. r0,r0,1 // decrement count of bytes to move addi r4,r4,1 subi r5,r5,1 // decrement buffer length remaining stb r8,0(r9) // pack into dest cmpwi cr1,r8,0 // 0-byte? addi r9,r9,1 beq cr1,L0found // byte was 0 bne Lbyteloop // r0!=0, source not yet aligned // Source is word aligned. Loop over words until end of buffer. We align // the source, rather than the dest, to avoid getting spurious page faults. // r4 = source ptr (word aligned) // r5 = length remaining in buffer // r6 = 0xFEFEFEFF // r7 = 0x80808080 // r9 = dest ptr (unaligned) Laligned: srwi. r8,r5,2 // get #words in buffer addi r0,r5,1 // if no words, compare rest of buffer beq Lbyteloop // r8==0, no words mtctr r8 // set up word loop count rlwinm r5,r5,0,0x3 // mask buffer length down to leftover bytes b LwordloopEnter // Move a word at a time, until one of two conditions: // - a zero byte is found // - end of buffer // At this point, registers are as follows: // r4 = source ptr (word aligned) // r5 = leftover bytes in buffer (0..3) // r6 = 0xFEFEFEFF // r7 = 0x80808080 // r9 = dest ptr (unaligned) // ctr = whole words left in buffer .align 5 // align inner loop, which is 8 words long Lwordloop: stw r8,0(r9) // pack word into destination addi r9,r9,4 LwordloopEnter: lwz r8,0(r4) // r8 <- next 4 source bytes addi r4,r4,4 add r10,r8,r6 // r10 <- word + 0xFEFEFEFF andc r12,r7,r8 // r12 <- ~word & 0x80808080 and. r11,r10,r12 // r11 <- nonzero iff word has a 0-byte bdnzt eq,Lwordloop // loop if ctr!=0 and cr0_eq beq Lleftovers // 0-byte not found in aligned words // Found a 0-byte. Store last word up to and including the 0, a byte at a time. // r8 = last word, known to have a 0-byte // r9 = dest ptr Lstorelastbytes: srwi. r0,r8,24 // right justify next byte and test for 0 slwi r8,r8,8 // shift next byte into position stb r0,0(r9) // pack into dest addi r9,r9,1 bne Lstorelastbytes // loop until 0 stored L0found: sub r3,r9,r3 // get #bytes stored, including 0 subi r3,r3,1 // don't count the 0 blr // return strlen(src) // 0-byte not found in aligned source words. There are up to 3 leftover source // bytes, hopefully the 0-byte is among them. // r4 = source ptr (word aligned) // r5 = leftover bytes in buffer (0..3) // r6 = 0xFEFEFEFF // r7 = 0x80808080 // r8 = last full word of source // r9 = dest ptr (unaligned) Lleftovers: stw r8,0(r9) // store last word addi r9,r9,4 addi r0,r5,1 // make sure r5 terminate byte loop (not r0) b Lbyteloop // Buffer full but 0-byte not found. Stuff a 0 into last byte of buffer. // r3 = start of buffer // r4 = ptr to next byte in source // r9 = ptr to first byte past end of buffer L0notfound: sub. r3,r9,r3 // get #bytes stored, ie original buffer length beq Lfind0 // skip if buffer 0-length li r0,0 // get a 0 stb r0,-1(r9) // always store 0-byte unless buffer was 0-length // Keep searching for 0-byte ending source, so we can return strlen(source). // Not optimized, since this is an error condition. // r3 = number of bytes already copied // r4 = ptr to next byte in source Lfind0: lbz r0,0(r4) // get next byte addi r4,r4,1 addi r3,r3,1 // increment strlen cmpwi r0,0 bne Lfind0 // loop if not 0 subi r3,r3,1 // don't count the 0-byte blr // return strlen(source)