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78 lines
1.8 KiB
78 lines
1.8 KiB
;----------------------------------------------------------------------------
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;
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; texdiff.inc
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;
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; Assembly macro for TextureDiff.
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;
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; Copyright (C) Microsoft Corporation, 1997.
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;
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;----------------------------------------------------------------------------
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IFNDEF __TEXDIFF_INC__
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__TEXDIFF_INC__ EQU 1
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;----------------------------------------------------------------------------
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;
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; TEXTURE_DIFF
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;
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; Computes difference of two texture coordinates and returns it on
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; the top of the FP stack.
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;
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; Destroys eax and ecx.
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;
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;----------------------------------------------------------------------------
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TEXTURE_DIFF MACRO fTb, fTa, iMode, fTmp
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LOCAL L_Exit, L_Ltz, L_Gtz, L_Zero, L_Straight
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; Start initial fTb - fTa computation.
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fld fTb
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fsub fTa
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; Check for wrapping.
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cmp iMode, 0
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jz L_Exit
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; Compute smaller of straight or wrapped difference.
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fst fTmp
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fld st(0)
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; Adjust straight difference according to sign to compute
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; wrapped difference.
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mov eax, fTmp
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cmp eax, 080000000h
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ja L_Ltz
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cmp eax, 0
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je L_Zero
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; Gtz
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fsub _g_fOne
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jmp L_Gtz
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L_Ltz:
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fadd _g_fOne
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L_Zero:
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and eax, 07fffffffh
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L_Gtz:
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fst fTmp
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mov ecx, fTmp
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and ecx, 07fffffffh
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; Pick smaller based on absolute values of differences.
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cmp eax, ecx
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jle L_Straight
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; Discard straight difference so wrapped difference is
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; returned.
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fxch st(1)
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L_Straight:
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; Discard wrapped difference so straight difference is
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; returned.
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fstp st(0)
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L_Exit:
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ENDM
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ENDIF
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