MdePkg/BaseMemoryLibOptDxe ARM: fix arithmetic bugs in CompareMem()
Fix two bugs:
- Erroneous shift of 2 in a bytes to bits conversion.
- Use reverse subtract rather than negate for value that is subsequently
used as operand #2 in a shift operation.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
diff --git a/MdePkg/Library/BaseMemoryLibOptDxe/Arm/CompareMem.S b/MdePkg/Library/BaseMemoryLibOptDxe/Arm/CompareMem.S
index 951d157..3aadeba 100644
--- a/MdePkg/Library/BaseMemoryLibOptDxe/Arm/CompareMem.S
+++ b/MdePkg/Library/BaseMemoryLibOptDxe/Arm/CompareMem.S
@@ -110,9 +110,9 @@
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.
+ lsl tmp1, tmp1, #3 // Bytes beyond alignment -> bits.
ldr data1, [src1], #4
- neg tmp1, tmp1 // Bits to alignment -32.
+ rsb tmp1, tmp1, #32 // Bits to alignment -32.
ldr data2, [src2], #4
mov tmp2, #~0
