From 450fe1bfa32643f7be38dbad89c8d32a539d5b66 Mon Sep 17 00:00:00 2001 From: Marcus Shawcroft <marcus.shawcroft@arm.com> Date: Thu, 17 Jan 2013 14:53:32 +0000 Subject: [PATCH] 2013-01-17 Marcus Shawcroft <marcus.shawcroft@linaro.org> * libc/machine/aarch64/strncmp.S: Correct arithmetic for argument N values close to the maximum representable value in an unsigned 64 bit value. --- newlib/ChangeLog | 6 ++++++ newlib/libc/machine/aarch64/strncmp.S | 31 ++++++++++++++++----------- 2 files changed, 25 insertions(+), 12 deletions(-) diff --git a/newlib/ChangeLog b/newlib/ChangeLog index 15123c0fc..d65758498 100644 --- a/newlib/ChangeLog +++ b/newlib/ChangeLog @@ -1,3 +1,9 @@ +2013-01-17 Marcus Shawcroft <marcus.shawcroft@linaro.org> + + * libc/machine/aarch64/strncmp.S: Correct arithmetic for + argument N values close to the maximum representable + value in an unsigned 64 bit value. + 2013-01-17 Marcus Shawcroft <marcus.shawcroft@linaro.org> * libc/machine/aarch64/strnlen.S: Correct arithmetic for diff --git a/newlib/libc/machine/aarch64/strncmp.S b/newlib/libc/machine/aarch64/strncmp.S index 6c2246dfb..0b90dd8a6 100644 --- a/newlib/libc/machine/aarch64/strncmp.S +++ b/newlib/libc/machine/aarch64/strncmp.S @@ -81,8 +81,10 @@ def_fn strncmp b.ne .Lmisaligned8 ands tmp1, src1, #7 b.ne .Lmutual_align - add limit_wd, limit, #7 - lsr limit_wd, limit_wd, #3 + /* Calculate the number of full and partial words -1. */ + sub limit_wd, limit, #1 /* limit != 0, so no underflow. */ + lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */ + /* 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. */ @@ -95,14 +97,14 @@ def_fn strncmp sub tmp1, data1, zeroones orr tmp2, data1, #REP8_7f eor diff, data1, data2 /* Non-zero if differences found. */ - csinv endloop, diff, xzr, ne /* Last Dword or differences. */ + csinv endloop, diff, xzr, pl /* Last Dword or differences. */ bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ ccmp endloop, #0, #0, eq b.eq .Lloop_aligned /* End of performance-critical section -- one 64B cache line. */ /* Not reached the limit, must have found the end or a diff. */ - cbnz limit_wd, .Lnot_limit + tbz limit_wd, #63, .Lnot_limit /* Limit % 8 == 0 => all bytes significant. */ ands limit, limit, #7 @@ -177,26 +179,31 @@ def_fn strncmp .Lmutual_align: /* Sources are mutually aligned, but are not currently at an alignment boundary. Round down the addresses and then mask off - the bytes that precede the start point. */ + the bytes that precede the start point. + We also need to adjust the limit calculations, but without + overflowing if the limit is near ULONG_MAX. */ bic src1, src1, #7 bic src2, src2, #7 - add limit, limit, tmp1 /* Adjust the limit for the extra. */ - lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */ ldr data1, [src1], #8 - neg tmp1, tmp1 /* Bits to alignment -64. */ + neg tmp3, tmp1, lsl #3 /* 64 - bits(bytes beyond align). */ ldr data2, [src2], #8 mov tmp2, #~0 + sub limit_wd, limit, #1 /* limit != 0, so no underflow. */ #ifdef __AARCH64EB__ /* Big-endian. Early bytes are at MSB. */ - lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ + lsl tmp2, tmp2, tmp3 /* Shift (tmp1 & 63). */ #else /* Little-endian. Early bytes are at LSB. */ - lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ + lsr tmp2, tmp2, tmp3 /* Shift (tmp1 & 63). */ #endif - add limit_wd, limit, #7 + and tmp3, limit_wd, #7 + lsr limit_wd, limit_wd, #3 + /* Adjust the limit. Only low 3 bits used, so overflow irrelevant. */ + add limit, limit, tmp1 + add tmp3, tmp3, tmp1 orr data1, data1, tmp2 orr data2, data2, tmp2 - lsr limit_wd, limit_wd, #3 + add limit_wd, limit_wd, tmp3, lsr #3 b .Lstart_realigned .Lret0: