Source code of Windows XP (NT5)
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;;; Copyright (C) Microsoft Corporation, 1986;; This Module contains Proprietary Information of Microsoft; Corporation and should be treated as Confidential.;subttl emdoc.asm - Documentationpage;--------------------------------------------------------------------;; WARNING - This may not be accurate for the stand-alone emulator.;; Glossary:; TOS - top-of-stack (e.g. simulated 8087 register stack); single - single precision real number in one of two formats:; memory (IEEE), internal (on stack, see below); double - double precision real number in one of two formats:; memory (IEEE), internal (on stack, see below).;; This source is organized into the following sections:; 1. Introductory documentation of instructions and data structures; 2. External routines, data segment, and const segment definitions; 3. Startup and terminate, utility truncTOS; 4. User memory macros; 5. Macros and procedures for stack push and pop, error handling; 6. Main entry point and effective address calculation routine;; Assumptions about segment usage:; SS = user's stack; DS = user's emulator data segment (not user's DS); ES = effective address segment for memory operands; = user's emulator data segment (all other times);; BASstk is DS offset of the stack base; CURstk is DS offset of the current register (TOS).; LIMstk is DS offset of LAST reg in stack;; CURerr has internal exception flag byte (<>0 iff exception occured).; UserControlWord has user set values; ControlWord has remapped version of UserControlWord; CWcntl (high byte of ControlWord) has Rounding, precision, Inf modes;; Macros:; PUSHST allocates a new 12 byte register, and POPST frees one.; Both return an address in SI and save all other 8086 registers.;; Five macros handle all data movement between user memory and local; memory or registers.;; Note standard forms:;; Bits are counted from least significant; bit 0 is 1's, bit 7 is 128's.;; IEEE format is used, naturally, for values in user memory:;; IEEE single precision:; +0: least significant byte of mantissa; +1: next sig. byte of mant.; +2: bits 6..0: most sig. bits of mant.; +2: bit 7: low order bit of exponent; +3: bits 6..0: rest of exponent; +3: bit 7: sign bit; mantissa does not include "hidden bit".; with hidden bit, mantissa value is 1.0 to 2.0; exponent is in biased form, with bias of 127; exponent of all 0's means a value of zero; exponent of all 1's means a value of "indefinite";; IEEE double precision:; +0: least significant byte of mantissa; +1..+5 next sig. bytes of mant.; +6: bits 3..0 (lo nibble): most sig. bits of mant.; +6: bits 7..4 (hi nibble): least sig. bits of exp.; +7: bits 6..0: most sig. bits of exponent; +7: bit 7: sign bit; mantissa does not include "hidden bit".; with hidden bit, mantissa value is 1.0 to 2.0; exponent is in biased form, with bias of 1023; exponent of all 0's means a value of zero or Denormal; exponent of all 1's means a value of NAN or Infinity
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