diff options
Diffstat (limited to 'sysdeps/aarch64/strcmp.S')
| -rw-r--r-- | sysdeps/aarch64/strcmp.S | 234 |
1 files changed, 125 insertions, 109 deletions
diff --git a/sysdeps/aarch64/strcmp.S b/sysdeps/aarch64/strcmp.S index d044c29e9b..77d7218dea 100644 --- a/sysdeps/aarch64/strcmp.S +++ b/sysdeps/aarch64/strcmp.S @@ -18,14 +18,14 @@ /* Assumptions: * - * ARMv8-a, AArch64 + * ARMv8-a, AArch64. + * MTE compatible. */ #include <sysdep.h> #define REP8_01 0x0101010101010101 #define REP8_7f 0x7f7f7f7f7f7f7f7f -#define REP8_80 0x8080808080808080 /* Parameters and result. */ #define src1 x0 @@ -39,146 +39,162 @@ #define data2w w3 #define has_nul x4 #define diff x5 +#define off1 x5 #define syndrome x6 -#define tmp1 x7 -#define tmp2 x8 -#define tmp3 x9 -#define zeroones x10 -#define pos x11 +#define tmp x6 +#define data3 x7 +#define zeroones x8 +#define shift x9 +#define off2 x10 + +/* On big-endian early bytes are at MSB and on little-endian LSB. + LS_FW means shifting towards early bytes. */ +#ifdef __AARCH64EB__ +# define LS_FW lsl +#else +# define LS_FW lsr +#endif - /* Start of performance-critical section -- one 64B cache line. */ -ENTRY_ALIGN(strcmp, 6) +/* NUL detection works on the principle that (X - 1) & (~X) & 0x80 + (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and + can be done in parallel across the entire word. + Since carry propagation makes 0x1 bytes before a NUL byte appear + NUL too in big-endian, byte-reverse the data before the NUL check. */ +ENTRY(strcmp) DELOUSE (0) DELOUSE (1) - eor tmp1, src1, src2 - mov zeroones, #REP8_01 - tst tmp1, #7 + sub off2, src2, src1 + mov zeroones, REP8_01 + and tmp, src1, 7 + tst off2, 7 b.ne L(misaligned8) - ands tmp1, src1, #7 - b.ne L(mutual_align) - /* NUL detection works on the principle that (X - 1) & (~X) & 0x80 - (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and - can be done in parallel across the entire word. */ + cbnz tmp, L(mutual_align) + + .p2align 4 + L(loop_aligned): - ldr data1, [src1], #8 - ldr data2, [src2], #8 + ldr data2, [src1, off2] + ldr data1, [src1], 8 L(start_realigned): - sub tmp1, data1, zeroones - orr tmp2, data1, #REP8_7f - eor diff, data1, data2 /* Non-zero if differences found. */ - bic has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ +#ifdef __AARCH64EB__ + rev tmp, data1 + sub has_nul, tmp, zeroones + orr tmp, tmp, REP8_7f +#else + sub has_nul, data1, zeroones + orr tmp, data1, REP8_7f +#endif + bics has_nul, has_nul, tmp /* Non-zero if NUL terminator. */ + ccmp data1, data2, 0, eq + b.eq L(loop_aligned) +#ifdef __AARCH64EB__ + rev has_nul, has_nul +#endif + eor diff, data1, data2 orr syndrome, diff, has_nul - cbz syndrome, L(loop_aligned) - /* End of performance-critical section -- one 64B cache line. */ - L(end): -#ifndef __AARCH64EB__ +#ifndef __AARCH64EB__ rev syndrome, syndrome rev data1, data1 - /* The MS-non-zero bit of the syndrome marks either the first bit - that is different, or the top bit of the first zero byte. - Shifting left now will bring the critical information into the - top bits. */ - clz pos, syndrome rev data2, data2 - lsl data1, data1, pos - lsl data2, data2, pos - /* But we need to zero-extend (char is unsigned) the value and then - perform a signed 32-bit subtraction. */ - lsr data1, data1, #56 - sub result, data1, data2, lsr #56 - RET -#else - /* For big-endian we cannot use the trick with the syndrome value - as carry-propagation can corrupt the upper bits if the trailing - bytes in the string contain 0x01. */ - /* However, if there is no NUL byte in the dword, we can generate - the result directly. We can't just subtract the bytes as the - MSB might be significant. */ - cbnz has_nul, 1f - cmp data1, data2 - cset result, ne - cneg result, result, lo - RET -1: - /* Re-compute the NUL-byte detection, using a byte-reversed value. */ - rev tmp3, data1 - sub tmp1, tmp3, zeroones - orr tmp2, tmp3, #REP8_7f - bic has_nul, tmp1, tmp2 - rev has_nul, has_nul - orr syndrome, diff, has_nul - clz pos, syndrome - /* The MS-non-zero bit of the syndrome marks either the first bit - that is different, or the top bit of the first zero byte. +#endif + clz shift, syndrome + /* The most-significant-non-zero bit of the syndrome marks either the + first bit that is different, or the top bit of the first zero byte. Shifting left now will bring the critical information into the top bits. */ - lsl data1, data1, pos - lsl data2, data2, pos + lsl data1, data1, shift + lsl data2, data2, shift /* But we need to zero-extend (char is unsigned) the value and then perform a signed 32-bit subtraction. */ - lsr data1, data1, #56 - sub result, data1, data2, lsr #56 - RET -#endif + lsr data1, data1, 56 + sub result, data1, data2, lsr 56 + ret + + .p2align 4 L(mutual_align): /* Sources are mutually aligned, but are not currently at an alignment boundary. Round down the addresses and then mask off - the bytes that preceed the start point. */ - bic src1, src1, #7 - bic src2, src2, #7 - lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */ - ldr data1, [src1], #8 - neg tmp1, tmp1 /* Bits to alignment -64. */ - ldr data2, [src2], #8 - mov tmp2, #~0 -#ifdef __AARCH64EB__ - /* Big-endian. Early bytes are at MSB. */ - lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ -#else - /* Little-endian. Early bytes are at LSB. */ - lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ -#endif - orr data1, data1, tmp2 - orr data2, data2, tmp2 + the bytes that precede the start point. */ + bic src1, src1, 7 + ldr data2, [src1, off2] + ldr data1, [src1], 8 + neg shift, src2, lsl 3 /* Bits to alignment -64. */ + mov tmp, -1 + LS_FW tmp, tmp, shift + orr data1, data1, tmp + orr data2, data2, tmp b L(start_realigned) L(misaligned8): /* Align SRC1 to 8 bytes and then compare 8 bytes at a time, always - checking to make sure that we don't access beyond page boundary in - SRC2. */ - tst src1, #7 - b.eq L(loop_misaligned) + checking to make sure that we don't access beyond the end of SRC2. */ + cbz tmp, L(src1_aligned) L(do_misaligned): - ldrb data1w, [src1], #1 - ldrb data2w, [src2], #1 - cmp data1w, #1 - ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */ + ldrb data1w, [src1], 1 + ldrb data2w, [src2], 1 + cmp data1w, 0 + ccmp data1w, data2w, 0, ne /* NZCV = 0b0000. */ b.ne L(done) - tst src1, #7 + tst src1, 7 b.ne L(do_misaligned) -L(loop_misaligned): - /* Test if we are within the last dword of the end of a 4K page. If - yes then jump back to the misaligned loop to copy a byte at a time. */ - and tmp1, src2, #0xff8 - eor tmp1, tmp1, #0xff8 - cbz tmp1, L(do_misaligned) - ldr data1, [src1], #8 - ldr data2, [src2], #8 - - sub tmp1, data1, zeroones - orr tmp2, data1, #REP8_7f - eor diff, data1, data2 /* Non-zero if differences found. */ - bic has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ +L(src1_aligned): + neg shift, src2, lsl 3 + bic src2, src2, 7 + ldr data3, [src2], 8 +#ifdef __AARCH64EB__ + rev data3, data3 +#endif + lsr tmp, zeroones, shift + orr data3, data3, tmp + sub has_nul, data3, zeroones + orr tmp, data3, REP8_7f + bics has_nul, has_nul, tmp + b.ne L(tail) + + sub off1, src2, src1 + + .p2align 4 + +L(loop_unaligned): + ldr data3, [src1, off1] + ldr data2, [src1, off2] +#ifdef __AARCH64EB__ + rev data3, data3 +#endif + sub has_nul, data3, zeroones + orr tmp, data3, REP8_7f + ldr data1, [src1], 8 + bics has_nul, has_nul, tmp + ccmp data1, data2, 0, eq + b.eq L(loop_unaligned) + + lsl tmp, has_nul, shift +#ifdef __AARCH64EB__ + rev tmp, tmp +#endif + eor diff, data1, data2 + orr syndrome, diff, tmp + cbnz syndrome, L(end) +L(tail): + ldr data1, [src1] + neg shift, shift + lsr data2, data3, shift + lsr has_nul, has_nul, shift +#ifdef __AARCH64EB__ + rev data2, data2 + rev has_nul, has_nul +#endif + eor diff, data1, data2 orr syndrome, diff, has_nul - cbz syndrome, L(loop_misaligned) b L(end) L(done): sub result, data1, data2 - RET + ret + END(strcmp) libc_hidden_builtin_def (strcmp) |