/* * Copyright (c) 2002 Apple Computer, Inc. All rights reserved. * * @APPLE_LICENSE_HEADER_START@ * * 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 /* We use mode-independent "g" opcodes such as "srgi". These expand * into word operations when targeting __ppc__, and into doubleword * operations when targeting __ppc64__. */ #include #define __APPLE_API_PRIVATE #include #undef __APPLE_API_PRIVATE // ***************** // * S T R N C A T * // ***************** // // char* strncat(char *dst, const char *src, size_t count); // // 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 extra 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. // // Note that "count" refers to the max number of bytes to _append_. // There is no limit to the number of bytes we will scan looking for // the end of the "dst" string. // // In 64-bit mode, this algorithm is doubleword parallel. .text .globl EXT(strncat) .align 5 LEXT(strncat) // char* strncat(char *dst, const char *src, size_t count); clrrgi r9,r3,LOG2_GPR_BYTES// align pointer by zeroing right LOG2_GPR_BYTES bits li r10,-1 // get 0xFFs lg r8,0(r9) // get word or doubleword with 1st operand byte rlwinm r11,r3,3,(GPR_BYTES-1)*8 // get starting bit position of operand #if defined(__ppc__) lis r6,hi16(0xFEFEFEFF) // start to generate 32-bit magic constants lis r7,hi16(0x80808080) srw r10,r10,r11 // create a mask of 0xFF bytes for operand in r8 ori r6,r6,lo16(0xFEFEFEFF) ori r7,r7,lo16(0x80808080) #else ld r6,_COMM_PAGE_MAGIC_FE(0) // get 0xFEFEFEFE FEFEFEFF from commpage ld r7,_COMM_PAGE_MAGIC_80(0) // get 0x80808080 80808080 from commpage srd r10,r10,r11 // create a mask of 0xFF bytes for operand in r8 #endif orc r8,r8,r10 // make sure bytes preceeding operand are nonzero b Lword0loopEnter // Loop over words or doublewords looking for 0-byte marking end of dest. // r4 = source ptr (unaligned) // r5 = count (unchanged so far) // r6 = 0xFEFEFEFF // r7 = 0x80808080 // r9 = dest ptr (aligned) .align 5 // align inner loops for speed Lword0loop: lgu r8,GPR_BYTES(r9) // r8 <- next dest word or doubleword Lword0loopEnter: 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 beq Lword0loop // loop until 0 found // Now we know one of the bytes in r8 is zero, we just have to figure out which one. // We have mapped 0 bytes to 0x80, and nonzero bytes to 0x00, with one exception: // 0x01 bytes preceeding the first zero are also mapped to 0x80. So we have to mask // out the 0x80s caused by 0x01s before searching for the 0x80 byte. Once the 0 is // found, we can start appending source. We align the source, which allows us to // avoid worrying about spurious page faults. // r4 = source ptr (unaligned) // r5 = count (unchanged so far) // r6 = 0xFEFEFEFF // r7 = 0x80808080 // r8 = word or doubleword with a 0-byte // r9 = ptr to the word or doubleword in r8 (aligned) // r11 = mapped word or doubleword slgi r10,r8,7 // move 0x01 bits (false hits) into 0x80 position andi. r0,r4,GPR_BYTES-1 // is source aligned? andc r11,r11,r10 // mask out false hits cntlzg r10,r11 // find 0 byte (r0 = 0, 8, 16, or 24) subfic r0,r0,GPR_BYTES // get #bytes to align r4 srwi r10,r10,3 // now r10 = 0, 1, 2, or 3 add r9,r9,r10 // now r9 points to the 0-byte in dest beq Laligned // skip if source already aligned // Copy min(r0,r5) bytes, until 0-byte. // 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: cmpgi r5,0 // buffer empty? (note: count is unsigned) 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 beqlr cr1 // byte was 0, so done bne Lbyteloop // r0!=0, source not yet aligned // Source is aligned. Loop over words or doublewords until 0-byte found // or end of buffer. // r4 = source ptr (aligned) // r5 = length remaining in buffer // r6 = 0xFEFEFEFF // r7 = 0x80808080 // r9 = dest ptr (unaligned) Laligned: srgi. r8,r5,LOG2_GPR_BYTES// get #words or doublewords in buffer addi r0,r5,1 // if no words, copy rest of buffer beq-- Lbyteloop // fewer than 4 bytes in buffer mtctr r8 // set up word loop count rlwinm r5,r5,0,GPR_BYTES-1 // mask buffer length down to leftover bytes b LwordloopEnter // Inner loop: move a word or doubleword 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 (aligned) // r5 = bytes leftover in buffer (0..GPR_BYTES-1) // r6 = 0xFEFEFEFF // r7 = 0x80808080 // r9 = dest ptr (unaligned) // ctr = whole words or doublewords left in buffer .align 5 // align inner loop, which is 8 words long Lwordloop: stg r8,0(r9) // pack word or doubleword into destination addi r9,r9,GPR_BYTES LwordloopEnter: lg r8,0(r4) // r8 <- next GPR_BYTES source bytes addi r4,r4,GPR_BYTES 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-- LcheckLeftovers // skip if 0-byte not found // Found a 0-byte. Store last word up to and including the 0, a byte at a time. // r8 = last word or doubleword, known to have a 0-byte // r9 = dest ptr Lstorelastbytes: srgi. r0,r8,GPR_BYTES*8-8 // right justify next byte and test for 0 slgi 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 blr // 0-byte not found while appending words to source. There might be up to // GPR_BYTES-1 "leftover" bytes to append, hopefully the 0-byte is in there. // r4 = source ptr (past word in r8) // r5 = bytes leftover in buffer (0..GPR_BYTES-1) // r6 = 0xFEFEFEFF // r7 = 0x80808080 // r8 = last word or doubleword of source, with no 0-byte // r9 = dest ptr (unaligned) LcheckLeftovers: stg r8,0(r9) // store last whole word or doubleword of source addi r9,r9,GPR_BYTES addi r0,r5,1 // let r5 (not r0) terminate byte loop b Lbyteloop // append last few bytes // 0-byte not found in source. We append a 0 anyway, even though it will // be past the end of the buffer. That's the way it's defined. // r9 = dest ptr L0notfound: li r0,0 stb r0,0(r9) // add a 0, past end of buffer blr