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- Committer: Will Newton
- Date: 2013-04-30 14:31:08 UTC
- Revision ID: will.newton@linaro.org-20130430143108-ww31c741wek8dnus
Split bionic reference code into A15 and A9 versions.
- files added:
- reference/bionic-a15
- reference/bionic-a9
- files removed:
- reference/bionic
- files modified:
- Makefile.am
added
removed
reference/bionic-a15/strcmp.S
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/*
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* Copyright (c) 2013 ARM Ltd
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the company may not be used to endorse or promote
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* products derived from this software without specific prior written
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* permission.
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*
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* THIS SOFTWARE IS PROVIDED BY ARM LTD ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
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* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifdef __ARMEB__
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#define S2LOMEM lsl
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#define S2LOMEMEQ lsleq
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#define S2HIMEM lsr
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#define MSB 0x000000ff
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#define LSB 0xff000000
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#define BYTE0_OFFSET 24
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#define BYTE1_OFFSET 16
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#define BYTE2_OFFSET 8
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#define BYTE3_OFFSET 0
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#else /* not __ARMEB__ */
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#define S2LOMEM lsr
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#define S2LOMEMEQ lsreq
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#define S2HIMEM lsl
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#define BYTE0_OFFSET 0
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#define BYTE1_OFFSET 8
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#define BYTE2_OFFSET 16
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#define BYTE3_OFFSET 24
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#define MSB 0xff000000
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#define LSB 0x000000ff
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#endif /* not __ARMEB__ */
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.syntax unified
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#if defined (__thumb__)
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.thumb
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.thumb_func
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#endif
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.globl strcmp
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.type strcmp,%function
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strcmp:
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.fnstart
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/* Use LDRD whenever possible. */
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/* The main thing to look out for when comparing large blocks is that
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the loads do not cross a page boundary when loading past the index
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of the byte with the first difference or the first string-terminator.
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For example, if the strings are identical and the string-terminator
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is at index k, byte by byte comparison will not load beyond address
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s1+k and s2+k; word by word comparison may load up to 3 bytes beyond
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k; double word - up to 7 bytes. If the load of these bytes crosses
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a page boundary, it might cause a memory fault (if the page is not mapped)
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that would not have happened in byte by byte comparison.
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If an address is (double) word aligned, then a load of a (double) word
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from that address will not cross a page boundary.
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Therefore, the algorithm below considers word and double-word alignment
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of strings separately. */
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/* High-level description of the algorithm.
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* The fast path: if both strings are double-word aligned,
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use LDRD to load two words from each string in every loop iteration.
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* If the strings have the same offset from a word boundary,
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use LDRB to load and compare byte by byte until
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the first string is aligned to a word boundary (at most 3 bytes).
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This is optimized for quick return on short unaligned strings.
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* If the strings have the same offset from a double-word boundary,
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use LDRD to load two words from each string in every loop iteration, as in the fast path.
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* If the strings do not have the same offset from a double-word boundary,
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load a word from the second string before the loop to initialize the queue.
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Use LDRD to load two words from every string in every loop iteration.
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Inside the loop, load the second word from the second string only after comparing
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the first word, using the queued value, to guarantee safety across page boundaries.
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* If the strings do not have the same offset from a word boundary,
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use LDR and a shift queue. Order of loads and comparisons matters,
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similarly to the previous case.
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* Use UADD8 and SEL to compare words, and use REV and CLZ to compute the return value.
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* The only difference between ARM and Thumb modes is the use of CBZ instruction.
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* The only difference between big and little endian is the use of REV in little endian
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to compute the return value, instead of MOV.
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*/
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.macro m_cbz reg label
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#ifdef __thumb2__
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cbz \reg, \label
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#else /* not defined __thumb2__ */
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cmp \reg, #0
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beq \label
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#endif /* not defined __thumb2__ */
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.endm /* m_cbz */
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.macro m_cbnz reg label
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#ifdef __thumb2__
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cbnz \reg, \label
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#else /* not defined __thumb2__ */
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cmp \reg, #0
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bne \label
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#endif /* not defined __thumb2__ */
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.endm /* m_cbnz */
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.macro init
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/* Macro to save temporary registers and prepare magic values. */
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subs sp, sp, #16
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strd r4, r5, [sp, #8]
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strd r6, r7, [sp]
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mvn r6, #0 /* all F */
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mov r7, #0 /* all 0 */
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.endm /* init */
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.macro magic_compare_and_branch w1 w2 label
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/* Macro to compare registers w1 and w2 and conditionally branch to label. */
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cmp \w1, \w2 /* Are w1 and w2 the same? */
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magic_find_zero_bytes \w1
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it eq
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cmpeq ip, #0 /* Is there a zero byte in w1? */
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bne \label
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.endm /* magic_compare_and_branch */
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.macro magic_find_zero_bytes w1
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/* Macro to find all-zero bytes in w1, result is in ip. */
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#if (defined (__ARM_FEATURE_DSP))
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uadd8 ip, \w1, r6
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sel ip, r7, r6
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#else /* not defined (__ARM_FEATURE_DSP) */
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/* __ARM_FEATURE_DSP is not defined for some Cortex-M processors.
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Coincidently, these processors only have Thumb-2 mode, where we can use the
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the (large) magic constant available directly as an immediate in instructions.
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Note that we cannot use the magic constant in ARM mode, where we need
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to create the constant in a register. */
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sub ip, \w1, #0x01010101
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bic ip, ip, \w1
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and ip, ip, #0x80808080
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#endif /* not defined (__ARM_FEATURE_DSP) */
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.endm /* magic_find_zero_bytes */
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.macro setup_return w1 w2
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#ifdef __ARMEB__
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mov r1, \w1
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mov r2, \w2
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#else /* not __ARMEB__ */
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rev r1, \w1
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rev r2, \w2
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#endif /* not __ARMEB__ */
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.endm /* setup_return */
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pld [r0, #0]
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pld [r1, #0]
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/* Are both strings double-word aligned? */
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orr ip, r0, r1
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tst ip, #7
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bne do_align
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/* Fast path. */
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init
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doubleword_aligned:
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/* Get here when the strings to compare are double-word aligned. */
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/* Compare two words in every iteration. */
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.p2align 2
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2:
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pld [r0, #16]
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pld [r1, #16]
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/* Load the next double-word from each string. */
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ldrd r2, r3, [r0], #8
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ldrd r4, r5, [r1], #8
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magic_compare_and_branch w1=r2, w2=r4, label=return_24
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magic_compare_and_branch w1=r3, w2=r5, label=return_35
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b 2b
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do_align:
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/* Is the first string word-aligned? */
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ands ip, r0, #3
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beq word_aligned_r0
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/* Fast compare byte by byte until the first string is word-aligned. */
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/* The offset of r0 from a word boundary is in ip. Thus, the number of bytes
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to read until the next word boundary is 4-ip. */
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bic r0, r0, #3
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ldr r2, [r0], #4
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lsls ip, ip, #31
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beq byte2
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bcs byte3
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byte1:
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ldrb ip, [r1], #1
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uxtb r3, r2, ror #BYTE1_OFFSET
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subs ip, r3, ip
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bne fast_return
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m_cbz reg=r3, label=fast_return
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byte2:
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ldrb ip, [r1], #1
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uxtb r3, r2, ror #BYTE2_OFFSET
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subs ip, r3, ip
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bne fast_return
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m_cbz reg=r3, label=fast_return
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byte3:
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ldrb ip, [r1], #1
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uxtb r3, r2, ror #BYTE3_OFFSET
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subs ip, r3, ip
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bne fast_return
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m_cbnz reg=r3, label=word_aligned_r0
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fast_return:
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mov r0, ip
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bx lr
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word_aligned_r0:
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init
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/* The first string is word-aligned. */
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/* Is the second string word-aligned? */
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ands ip, r1, #3
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bne strcmp_unaligned
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word_aligned:
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/* The strings are word-aligned. */
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/* Is the first string double-word aligned? */
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tst r0, #4
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beq doubleword_aligned_r0
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/* If r0 is not double-word aligned yet, align it by loading
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and comparing the next word from each string. */
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ldr r2, [r0], #4
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ldr r4, [r1], #4
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magic_compare_and_branch w1=r2 w2=r4 label=return_24
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doubleword_aligned_r0:
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/* Get here when r0 is double-word aligned. */
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/* Is r1 doubleword_aligned? */
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tst r1, #4
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beq doubleword_aligned
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/* Get here when the strings to compare are word-aligned,
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r0 is double-word aligned, but r1 is not double-word aligned. */
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/* Initialize the queue. */
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ldr r5, [r1], #4
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/* Compare two words in every iteration. */
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.p2align 2
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3:
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pld [r0, #16]
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pld [r1, #16]
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/* Load the next double-word from each string and compare. */
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ldrd r2, r3, [r0], #8
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magic_compare_and_branch w1=r2 w2=r5 label=return_25
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ldrd r4, r5, [r1], #8
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magic_compare_and_branch w1=r3 w2=r4 label=return_34
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b 3b
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.macro miscmp_word offsetlo offsethi
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/* Macro to compare misaligned strings. */
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/* r0, r1 are word-aligned, and at least one of the strings
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is not double-word aligned. */
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/* Compare one word in every loop iteration. */
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/* OFFSETLO is the original bit-offset of r1 from a word-boundary,
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OFFSETHI is 32 - OFFSETLO (i.e., offset from the next word). */
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/* Initialize the shift queue. */
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ldr r5, [r1], #4
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/* Compare one word from each string in every loop iteration. */
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.p2align 2
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7:
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ldr r3, [r0], #4
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S2LOMEM r5, r5, #\offsetlo
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magic_find_zero_bytes w1=r3
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cmp r7, ip, S2HIMEM #\offsetlo
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and r2, r3, r6, S2LOMEM #\offsetlo
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it eq
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cmpeq r2, r5
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bne return_25
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ldr r5, [r1], #4
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cmp ip, #0
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eor r3, r2, r3
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S2HIMEM r2, r5, #\offsethi
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it eq
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cmpeq r3, r2
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bne return_32
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b 7b
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.endm /* miscmp_word */
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strcmp_unaligned:
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/* r0 is word-aligned, r1 is at offset ip from a word. */
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/* Align r1 to the (previous) word-boundary. */
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bic r1, r1, #3
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/* Unaligned comparison word by word using LDRs. */
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cmp ip, #2
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beq miscmp_word_16 /* If ip == 2. */
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bge miscmp_word_24 /* If ip == 3. */
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miscmp_word offsetlo=8 offsethi=24 /* If ip == 1. */
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miscmp_word_16: miscmp_word offsetlo=16 offsethi=16
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miscmp_word_24: miscmp_word offsetlo=24 offsethi=8
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return_32:
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setup_return w1=r3, w2=r2
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b do_return
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return_34:
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setup_return w1=r3, w2=r4
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b do_return
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return_25:
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setup_return w1=r2, w2=r5
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b do_return
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return_35:
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setup_return w1=r3, w2=r5
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b do_return
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return_24:
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setup_return w1=r2, w2=r4
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do_return:
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#ifdef __ARMEB__
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mov r0, ip
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#else /* not __ARMEB__ */
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rev r0, ip
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#endif /* not __ARMEB__ */
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/* Restore temporaries early, before computing the return value. */
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ldrd r6, r7, [sp]
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ldrd r4, r5, [sp, #8]
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adds sp, sp, #16
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/* There is a zero or a different byte between r1 and r2. */
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/* r0 contains a mask of all-zero bytes in r1. */
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/* Using r0 and not ip here because cbz requires low register. */
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m_cbz reg=r0, label=compute_return_value
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clz r0, r0
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/* r0 contains the number of bits on the left of the first all-zero byte in r1. */
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rsb r0, r0, #24
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/* Here, r0 contains the number of bits on the right of the first all-zero byte in r1. */
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lsr r1, r1, r0
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lsr r2, r2, r0
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compute_return_value:
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movs r0, #1
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cmp r1, r2
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/* The return value is computed as follows.
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If r1>r2 then (C==1 and Z==0) and LS doesn't hold and r0 is #1 at return.
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If r1<r2 then (C==0 and Z==0) and we execute SBC with carry_in=0,
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which means r0:=r0-r0-1 and r0 is #-1 at return.
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If r1=r2 then (C==1 and Z==1) and we execute SBC with carry_in=1,
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which means r0:=r0-r0 and r0 is #0 at return.
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(C==0 and Z==1) cannot happen because the carry bit is "not borrow". */
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it ls
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sbcls r0, r0, r0
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bx lr
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.fnend
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.size strcmp, .-strcmp
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