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1 | ; $Id: ASMBitLastSetU16.asm 76553 2019-01-01 01:45:53Z vboxsync $
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2 | ;; @file
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3 | ; BiosCommonCode - ASMBitLastSetU16() - borrowed from IPRT.
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4 | ;
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5 |
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6 | ;
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7 | ; Copyright (C) 2006-2019 Oracle Corporation
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8 | ;
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9 | ; This file is part of VirtualBox Open Source Edition (OSE), as
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10 | ; available from http://www.virtualbox.org. This file is free software;
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11 | ; you can redistribute it and/or modify it under the terms of the GNU
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12 | ; General Public License (GPL) as published by the Free Software
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13 | ; Foundation, in version 2 as it comes in the "COPYING" file of the
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14 | ; VirtualBox OSE distribution. VirtualBox OSE is distributed in the
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15 | ; hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
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16 | ;
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17 |
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18 |
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19 | ;*******************************************************************************
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20 | ;* Header Files *
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21 | ;*******************************************************************************
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22 | public _ASMBitLastSetU16
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23 |
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24 | .8086
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25 |
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26 | _TEXT segment public 'CODE' use16
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27 | assume cs:_TEXT
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28 |
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29 |
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30 | ;;
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31 | ; Finds the last bit which is set in the given 16-bit integer.
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32 | ;
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33 | ; Bits are numbered from 1 (least significant) to 16.
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34 | ;
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35 | ; @returns (ax) index [1..16] of the last set bit.
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36 | ; @returns (ax) 0 if all bits are cleared.
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37 | ; @param u16 Integer to search for set bits.
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38 | ;
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39 | ; @cproto DECLASM(unsigned) ASMBitLastSetU16(uint32_t u16);
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40 | ;
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41 | _ASMBitLastSetU16 proc
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42 | .8086
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43 | push bp
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44 | mov bp, sp
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45 |
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46 | mov cx, [bp + 2 + 2]
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47 | test cx, cx ; check if zero (eliminates checking dec ax result)
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48 | jz return_zero
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49 |
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50 | mov ax, 16
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51 | next_bit:
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52 | shl cx, 1
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53 | jc return
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54 | dec ax
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55 | jmp next_bit
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56 |
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57 | return_zero:
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58 | xor ax, ax
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59 | return:
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60 | pop bp
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61 | ret
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62 | _ASMBitLastSetU16 endp
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63 |
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64 | _TEXT ends
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65 | end
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66 |
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