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comments (documentation about instruction formats)

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Roberto Ierusalimschy 2017-09-18 13:07:54 -03:00
parent 022e4427cf
commit e0c0e2ee14
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lopcodes.h
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@ -1,5 +1,5 @@
/*
** $Id: lopcodes.h,v 1.157 2017/09/13 19:50:08 roberto Exp roberto $
** $Id: lopcodes.h,v 1.158 2017/09/15 14:19:06 roberto Exp roberto $
** Opcodes for Lua virtual machine
** See Copyright Notice in lua.h
*/
@ -11,21 +11,20 @@
/*===========================================================================
We assume that instructions are unsigned numbers.
We assume that instructions are unsigned 32-bit integers.
All instructions have an opcode in the first 6 bits.
Instructions can have the following fields:
'A' : 8 bits
'B' : 9 bits
'C' : 9 bits
'Ax' : 26 bits ('A', 'B', and 'C' together)
'Bx' : 18 bits ('B' and 'C' together)
'sBx' : signed Bx
Instructions can have the following formats:
A signed argument is represented in excess K; that is, the number
value is the unsigned value minus K. K is exactly the maximum value
for that argument (so that -max is represented by 0, and +max is
represented by 2*max), which is half the maximum for the corresponding
unsigned argument.
3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
iABC | C(9) | | B(9) | | A(8) | | Op(6) |
iABx | Bx(18) | | A(8) | | Op(6) |
iAsBx | sBx (signed)(18) | | A(8) | | Op(6) |
iAx | Ax(26) | | Op(6) |
A signed argument is represented in excess K: the represented value is
the written unsigned value minus K, where K is half the maximum for the
corresponding unsigned argument.
===========================================================================*/