1 files changed, 118 insertions, 0 deletions
diff --git a/roms/edk2/MdePkg/Library/BaseMemoryLibOptDxe/Arm/CompareMem.asm b/roms/edk2/MdePkg/Library/BaseMemoryLibOptDxe/Arm/CompareMem.asm
new file mode 100644
index 000000000..27a1efc8c
--- /dev/null
+++ b/roms/edk2/MdePkg/Library/BaseMemoryLibOptDxe/Arm/CompareMem.asm
@@ -0,0 +1,118 @@
+;
+; Copyright (c) 2013 - 2016, Linaro Limited
+; All rights reserved.
+; SPDX-License-Identifier: BSD-2-Clause-Patent
+;
+
+; Parameters and result.
+#define src1      r0
+#define src2      r1
+#define limit     r2
+#define result    r0
+
+; Internal variables.
+#define data1     r3
+#define data2     r4
+#define limit_wd  r5
+#define diff      r6
+#define tmp1      r7
+#define tmp2      r12
+#define pos       r8
+#define mask      r14
+
+    EXPORT  InternalMemCompareMem
+    THUMB
+    AREA    CompareMem, CODE, READONLY
+
+InternalMemCompareMem
+    push    {r4-r8, lr}
+    eor     tmp1, src1, src2
+    tst     tmp1, #3
+    bne     Lmisaligned4
+    ands    tmp1, src1, #3
+    bne     Lmutual_align
+    add     limit_wd, limit, #3
+    nop.w
+    lsr     limit_wd, limit_wd, #2
+
+    ; Start of performance-critical section  -- one 32B cache line.
+Lloop_aligned
+    ldr     data1, [src1], #4
+    ldr     data2, [src2], #4
+Lstart_realigned
+    subs    limit_wd, limit_wd, #1
+    eor     diff, data1, data2        ; Non-zero if differences found.
+    cbnz    diff, L0
+    bne     Lloop_aligned
+    ; End of performance-critical section  -- one 32B cache line.
+
+    ; Not reached the limit, must have found a diff.
+L0
+    cbnz    limit_wd, Lnot_limit
+
+    // Limit % 4 == 0 => all bytes significant.
+    ands    limit, limit, #3
+    beq     Lnot_limit
+
+    lsl     limit, limit, #3              // Bits -> bytes.
+    mov     mask, #~0
+    lsl     mask, mask, limit
+    bic     data1, data1, mask
+    bic     data2, data2, mask
+
+    orr     diff, diff, mask
+
+Lnot_limit
+    rev     diff, diff
+    rev     data1, data1
+    rev     data2, data2
+
+    ; The MS-non-zero bit of DIFF marks either the first bit
+    ; that is different, or the end of the significant data.
+    ; Shifting left now will bring the critical information into the
+    ; top bits.
+    clz     pos, diff
+    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, #28
+    sub     result, data1, data2, lsr #28
+    pop     {r4-r8, pc}
+
+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.
+    bic     src1, src1, #3
+    bic     src2, src2, #3
+    add     limit, limit, tmp1          ; Adjust the limit for the extra.
+    lsl     tmp1, tmp1, #2              ; Bytes beyond alignment -> bits.
+    ldr     data1, [src1], #4
+    neg     tmp1, tmp1                  ; Bits to alignment -32.
+    ldr     data2, [src2], #4
+    mov     tmp2, #~0
+
+    ; Little-endian.  Early bytes are at LSB.
+    lsr     tmp2, tmp2, tmp1            ; Shift (tmp1 & 31).
+    add     limit_wd, limit, #3
+    orr     data1, data1, tmp2
+    orr     data2, data2, tmp2
+    lsr     limit_wd, limit_wd, #2
+    b       Lstart_realigned
+
+Lmisaligned4
+    sub     limit, limit, #1
+L1
+    // Perhaps we can do better than this.
+    ldrb    data1, [src1], #1
+    ldrb    data2, [src2], #1
+    subs    limit, limit, #1
+    it      cs
+    cmpcs   data1, data2
+    beq     L1
+    sub     result, data1, data2
+    pop     {r4-r8, pc}
+
+    END