/* * 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 #define __APPLE_API_PRIVATE #include #undef __APPLE_API_PRIVATE /* 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 // ***************** // * S T R N C P Y * // ***************** // // char* strncpy(const char *dst, const char *src, size_t len); // // 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. // // This algorithm is doubleword parallel in 64-bit mode. .text .globl EXT(strncpy) .align 5 LEXT(strncpy) // char* strncpy(const char *dst, const char *src, size_t len)); andi. r0,r4,GPR_BYTES-1 // is source aligned? #if defined(__ppc__) lis r6,hi16(0xFEFEFEFF) // start to generate 32-bit magic constants lis r7,hi16(0x80808080) 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 #endif mr r9,r3 // use r9 for dest ptr (must return r3 intact) add r2,r3,r5 // remember where end of buffer is beq Laligned // source is aligned subfic r0,r0,GPR_BYTES // r0 <- #bytes to align source // Copy min(r0,r5) bytes, until 0-byte. // r0 = #bytes we propose to copy (NOTE: must be >0) // r2 = ptr to 1st byte not in buffer // 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: length is unsigned) beqlr-- // 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 cmpwi cr1,r8,0 // 0-byte? stb r8,0(r9) // pack into dest addi r9,r9,1 beq cr1,L0found // byte was 0 bne Lbyteloop // r0!=0, source not yet aligned // Source is aligned. Loop over words or doublewords until end of buffer. Note that // we have aligned the source, rather than the dest, in order to avoid spurious // page faults. // r2 = ptr to 1st byte not in 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 none, compare rest of buffer beq-- Lbyteloop // r8==0, no words mtctr r8 // set up word loop count rlwinm r5,r5,0,GPR_BYTES-1 // mask buffer length down to leftover bytes b Lwordloop // Move a word or a doubleword at a time, until one of two conditions: // - a zero byte is found // - end of buffer // At this point, registers are as follows: // r2 = ptr to 1st byte not in buffer // r4 = source ptr (aligned) // r5 = leftover bytes 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: lg r8,0(r4) // r8 <- next 4 or 8 source bytes addi r9,r9,GPR_BYTES // bump dest addr while we wait for data addi r4,r4,GPR_BYTES add r10,r8,r6 // r10 <- word + 0xFEFEFEFF andc r12,r7,r8 // r12 <- ~word & 0x80808080 stg r8,-GPR_BYTES(r9) // pack word or doubleword into destination and. r11,r10,r12 // r11 <- nonzero iff word has a 0-byte bdnzt eq,Lwordloop // loop if ctr!=0 and cr0_eq addi r0,r5,1 // if no 0-byte found... beq-- Lbyteloop // ...fill rest of buffer a byte at a time // Found a 0-byte, point to following byte with r9. slgi r0,r8,7 // move 0x01 false hit bits to 0x80 position andc r11,r11,r0 // mask out false hits cntlzg r0,r11 // find the 0-byte (r0 = 0,8,16, or 24) srwi r0,r0,3 // now r0 = 0, 1, 2, or 3 (0..7 if 64-bit) subfic r0,r0,GPR_BYTES-1 // now r0 = 3, 2, 1, or 0 sub r9,r9,r0 // now r9 points one past the 0-byte // Zero rest of buffer, if any. We use the commpage bzero() routine. // r2 = ptr to 1st byte not in buffer // r9 = ptr to 1st byte to zero // // NB: commpage bzero() preserves r10-r12 by contract. L0found: mflr r12 // save return mr r11,r3 // save original dest ptr sub r4,r2,r9 // #bytes to zero (ie, rest of buffer) mr r3,r9 // point to 1st byte to zero bla _COMM_PAGE_BZERO mtlr r12 // restore our return mr r3,r11 // restore ptr to original dest blr