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replace and with test in boot0 to remove a mov

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pantonshire committed 2024-07-22 08:50:02 +01:00
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commit 15d97a8d55
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@@ -104,12 +104,11 @@ main:
; - If each entry is smaller than a sector, an integer number of them will fit into a sector. ; - If each entry is smaller than a sector, an integer number of them will fit into a sector.
or eax, eax ; Test size != 0 because 128 * 2^n != 0 or eax, eax ; Test size != 0 because 128 * 2^n != 0
jz panic jz panic
and eax, 127 ; Test size is a multiple of 128 test eax, 127 ; Test size is a multiple of 128
jnz panic jnz panic
; Use the (n & (n - 1)) == 0 trick to test if the entry size is a power of 2. Since we already ; Use the (n & (n - 1)) == 0 trick to test if the entry size is a power of 2. Since we already
; know it's a nonzero multiple of 128, if size is a power of 2 then size = 128 * 2^n holds. ; know it's a nonzero multiple of 128, if size is a power of 2 then size = 128 * 2^n holds.
; Therefore we don't need to bother dividing by 128 first (shr 7), which saves a couple of bytes. ; Therefore we don't need to bother dividing by 128 first (shr 7), which saves a couple of bytes.
mov eax, ebx
mov ecx, ebx mov ecx, ebx
dec ecx dec ecx
and ecx, eax and ecx, eax