/* * 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 // we need the defs for cr7_eq etc #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 M P * // ***************** // // int strncmp(const char *s1, const char *s2, size_t len); // // We optimize the compare by doing it word parallel. This introduces // a complication: if we blindly did word loads from both sides until // finding a difference (or 0), we might get a spurious page fault by // reading bytes past the difference. To avoid this, we never do a "lwz" // that crosses a page boundary. // // 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 routine is doubleword parallel in 64-bit mode. .text .globl EXT(strncmp) .align 5 LEXT(strncmp) // int strncmp(const char *s1,const char *s2,size_t len); cmplgi cr1,r5,GPR_BYTES*2 // buffer too short to bother? (WARNING: cr1 is used later) andi. r0,r3,GPR_BYTES-1 // is LHS aligned? subi r3,r3,GPR_BYTES // we use "lgu" in the inner loops subi r4,r4,GPR_BYTES blt cr1,Lshort // short buffer, just compare a byte at a time #if defined(__ppc__) lis r2,hi16(0xFEFEFEFF) // start to generate 32-bit magic constants lis r6,hi16(0x80808080) ori r2,r2,lo16(0xFEFEFEFF) ori r6,r6,lo16(0x80808080) #else ld r2,_COMM_PAGE_MAGIC_FE(0) // get 0xFEFEFEFE FEFEFEFF from commpage ld r6,_COMM_PAGE_MAGIC_80(0) // get 0x80808080 80808080 from commpage #endif beq Laligned // LHS is aligned subfic r0,r0,GPR_BYTES // r0 <- #bytes to align LHS mtctr r0 sub r5,r5,r0 // adjust length b Lbyteloop // Handle short operands or end-of-buffer. // r3 = LHS ptr - GPR_BYTES (unaligned) // r4 = RHS ptr - GPR_BYTES (unaligned) // r5 = length remaining in buffer (0..GPR_BYTES*2-1) // cr1 = blt set Lshort: cmpgi r5,0 // buffer null? mtctr r5 // assume not null, set up for loop bne Lbyteloop // buffer not null li r3,0 // if buffer null, say "equal" blr // We're at a RHS page boundary. Compare GPR_BYTES bytes in order to cross the page // but still keep the LHS ptr word-aligned. // r2 = 0xFEFEFEFF // r3 = LHS ptr - GPR_BYTES (aligned) // r4 = RHS ptr - GPR_BYTES (unaligned) // r5 = length remaining in buffer (may be 0) // r6 = 0x80808080 Lcrosspage: cmplgi cr1,r5,GPR_BYTES*2 // not enough left in buffer for word compares? li r0,GPR_BYTES // get #bytes to cross RHS page blt cr1,Lshort // buffer is about to end mtctr r0 // set up to compare GPR_BYTES bytes sub r5,r5,r0 // adjust length b Lbyteloop // Compare bytes, until 0-byte or difference found. // r2 = 0xFEFEFEFF (if cr1 bge) // r3 = LHS ptr - GPR_BYTES (unaligned) // r4 = RHS ptr - GPR_BYTES (unaligned) // r5 = length remaining in buffer (may be 0) // r6 = 0x80808080 (if cr1 bge) // cr1 = blt if this is end of buffer .align 5 // align inner loop, which is 8 words long Lbyteloop: lbz r7,GPR_BYTES(r3) // next LHS byte addi r3,r3,1 lbz r8,GPR_BYTES(r4) // next RHS byte addi r4,r4,1 cmpwi cr0,r7,0 // zero? cmpw cr7,r7,r8 // equal? crandc cr0_eq,cr7_eq,cr0_eq// set cr0_eq if equal and not 0 bdnzt eq,Lbyteloop // loop until different, 0, or (ctr==0) bne Ldifferent // done if bytes differ or are 0 blt cr1,Ldifferent // done if buffer end (ie, if r5==0) // LHS is now aligned. Loop over words or doublewords until end of RHS page // or buffer. When we get to the end of the page, we compare GPR_BYTES bytes, // so that we keep the LHS aligned. // r2 = 0xFEFEFEFF // r3 = LHS ptr - GPR_BYTES (aligned) // r4 = RHS ptr - GPR_BYTES (unaligned) // r5 = length remaining in buffer (may be 0) // r6 = 0x80808080 Laligned: addi r9,r4,GPR_BYTES // restore true address of next RHS byte rlwinm r9,r9,0,0xFFF // get RHS offset in page subfic r0,r9,4096 // get #bytes left in RHS page subfc r7,r0,r5 // *** subfe r8,r5,r5 // * r9 <- min(r0,r5), and r7,r7,r8 // * using algorithm in Compiler Writer's Guide add r9,r0,r7 // *** srgi. r8,r9,LOG2_GPR_BYTES// get #words or doublewords we can compare beq-- Lcrosspage // none so advance to next RHS page slgi r9,r8,LOG2_GPR_BYTES// get #bytes we will be comparing in parallel loop mtctr r8 // set up loop count sub r5,r5,r9 // decrement length remaining b Lwordloop // Inner loop: compare a word or doubleword at a time, until one of three conditions: // - a difference is found // - a zero byte is found // - end of count (ie, end of buffer or RHS page, whichever is first) // At this point, registers are as follows: // r2 = 0xFEFEFEFF // r3 = LHS ptr - GPR_BYTES (aligned) // r4 = RHS ptr - GPR_BYTES (unaligned) // r5 = length remaining in buffer (may be 0) // r6 = 0x80808080 // ctr = count of words or doublewords until end of buffer or RHS page .align 5 // align inner loop, which is 8 words long Lwordloop: lgu r7,GPR_BYTES(r3) // r7 <- next 4 or 8 LHS bytes lgu r8,GPR_BYTES(r4) // r8 <- next 4 or 8 RHS bytes add r10,r7,r2 // r10 <- LHS + 0xFEFEFEFF andc r12,r6,r7 // r12 <- ~LHS & 0x80808080 xor r11,r7,r8 // r11 <- compare the words and r9,r10,r12 // r9 <- nonzero iff LHS has a 0-byte or. r12,r9,r11 // combine difference and 0-test vectors bdnzt eq,Lwordloop // loop if ctr!=0 and cr0_eq beq-- Lcrosspage // skip if buffer or page end reached // Found differing bytes and/or a 0-byte. Determine which comes first, and // subtract the bytes to compute the return value. We also need to mask out the // false hits in the 0-byte test, which consist of 0x01 bytes that preceed // the 0-byte. slgi r0,r7,7 // move 0x01 bits in LHS into position 0x80 andc r9,r9,r0 // mask out the false 0-hits from 0x01 bytes or r11,r11,r9 // recompute difference vector cntlzg r0,r11 // find 1st difference (r0 = 0..31 or 63) rlwinm r9,r0,0,0x38 // byte align bit offset (r9 = 0,8,16, or 24) addi r0,r9,8 // now, r0 = 8, 16, 24, or 32 #if defined(__ppc__) rlwnm r7,r7,r0,24,31 // right justify differing bytes and mask off rest rlwnm r8,r8,r0,24,31 #else rldcl r7,r7,r0,56 // right justify differing bytes and mask off rest rldcl r8,r8,r0,56 #endif Ldifferent: // bytes in r7 and r8 differ or are 0 sub r3,r7,r8 // compute return value blr