source: xtideuniversalbios/trunk/Assembly_Library/Src/Display/DisplayFormatCompressed.asm@ 205

; Project name  :   Assembly Library
; Description   :   Functions for displaying formatted strings.
;                   ** Compressed Strings edition **
;                   This is a plug replacement for DisplayFormat.asm,
;                   working instead with precompiled and slightly compressed strings.
;
; Strings are compressed in a simple manner:
;   1. The two most common characters, space and null, are removed
;   2. Format specifiers are reduced to a single byte, including length information
;
; Format of bytes in the string are:
;     01 xxxxxx     Character in x plus StringsCompressed_NormalBase
;     10 xxxxxx     Character in x plus StringsCompressed_NormalBase, followed by a null (last character)
;     11 xxxxxx     Character in x plus StringsCompressed_NormalBase, followed by a space
;     00 1 yyyyy    Character/Format in lookup table StringsCopmressed_TranslatesAndFormats
;     00 0 yyyyy    Character/Format in lookup table StringsCompressed_TranslatesAndFormats, followed by a null
;
; StringsCompressed_NormalBase is defined by the compressor, but is usually around 0x40,
; which gives a range of 0x40 to 0x7f, or roughly the upper and lower case letters.
;
; StringsCompressed_TranslatesAndFormats is a lookup table with the first few bytes being translation
; characters, and the last few bytes being format jump offsets from DisplayFormatCompressed_BaseFormatOffset.
; The dividing line is defined by StringsCompressed_FormatsBegin
;
; The assignments of the first two bits above is not by accident.  The translates/format branch is 00
; which is easy to test for.  The '01' for "normal" (no null or space) and '001' for translates/format "normal"
; match, allowing the translates/format codes to be shifted left by 1 and then tested with the same instructions.
;
; It is always possible to say that a null character follows the current character - thus there is
; no way (nor need) to specify a zero character.
;
; Note that this code is optimized for size, not speed.  Since this code is used only during initialization
; and only for the user interface, small performance hits should not be noticed.  It will seem odd to do so
; much "preload", just in case a branch is taken, but that is cheaper (in size) than adding additional branches.
;

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; Format Handlers
;
; Names of format handlers are DisplayFormatCompressed_Format_* where * is
; replaced with the format code after the '%' in the original string,
; with '-' replaced with '_'.
;
;   Parameters:
;       DS:     BDA segment (zero)
;       AX:     Parameter to Format
;       ES:DI:  Ptr to cursor location in video RAM
;   Returns:
;       DI:     Updated offset to video RAM
;   Corrupts registers:
;       AX, BX, CX, DX, SI
;--------------------------------------------------------------------

;
; The following routines do not need any pre or post processing and can be jumped to directly.
; Note that they need to be within 256 bytes of DisplayFormatCompressed_BaseFormatOffset
;
%define DisplayFormatCompressed_Format_c DisplayPrint_CharacterFromAL
%define DisplayFormatCompressed_Format_nl DisplayPrint_Newline_FormatAdjustBP
%define DisplayFormatCompressed_Format_s DisplayFormat_ParseCharacters_FromAX

DisplayFormatCompressed_Format_A:
    mov     [VIDEO_BDA.displayContext+DISPLAY_CONTEXT.bAttribute], al
DisplayFormatCompressed_ret:            ; jump target for other routines who need a "ret"
    ret

DisplayFormatCompressed_Format_x:
DisplayFormatCompressed_Format_5_x:
    mov     si,16                       ; hex output, change base to 16
    mov     bx,(04<<8) + 'h'            ; 4 bytes, with postfix character 'h' to emit
                                        ; (note that the count includes the 'h')
    jmp     DisplayFormatCompressed_Format_u

DisplayFormatCompressed_Format_2_I:
    mov     si,g_szDashForZero          ; preload dash string in case we jump
    test    ax,ax                       ; if parameter equals zero, emit dash string instead
    jz      DisplayFormat_ParseCharacters
    ; fall through

DisplayFormatCompressed_Format_2_u:
    mov     bh,2                        ; only two characters (instead of the default 5)
    ; fall through

DisplayFormatCompressed_Format_u:
DisplayFormatCompressed_Format_5_u:
    push    bx                          ; push postfix character - either a zero (default) or a 'h'
    mov     bl,bh                       ; preserve character count for .PrintLoop

.DivLoop:
    xor     dx, dx                      ; Zero DX for division
    div     si                          ; DX:AX / 10 => AX=quot, DX=rem
    push    dx                          ; Push digit

    dec     bh
    jnz     .DivLoop

.PrintLoop:
    pop     ax                          ; Pop digit, postfix character on last iteration

    dec     bl                          ; on second to last iteration, emit digit whether it is zero or not
    jz      .PrintDigit

    js      short DisplayPrint_CharacterFromAL  ; on last iteration, emit postfix character
                                                ; if it is zero, DisplayPrint_CharacterFromAL will not emit

    or      bh, al                      ; skip leading zeros, bh keeps track if we have emitted anything non-zero
    jnz     .PrintDigit                 ; note that bh starts at zero, from the loop above

    test    ch,2                        ; are we padding with leading spaces?
    jnz     .PrintLoop                  ; test the even/odd of the format byte in the string

    mov     al, 89h                     ; emit space

.PrintDigit:
    add     al, 90h                     ; Convert binary digit in AL to ASCII hex digit (0 - 9 or A - F)
    daa
    adc     al, 40h
    daa

    call    DisplayPrint_CharacterFromAL

    jmp     .PrintLoop


;--------------------------------------------------------------------
; DisplayFormat_ParseCharacters
;   Parameters:
;       DS:     BDA segment (zero)
;       SS:BP:  Pointer to first format parameter (-=2 updates to next parameter)
;       CS:SI:  Pointer to string to format
;       ES:DI:  Ptr to cursor location in video RAM
;   Returns:
;       CS:SI:  Ptr to end of format string (ptr to one past NULL)
;       DI:     Updated offset to video RAM
;   Corrupts registers:
;       AX, BX, CX, DX, BP
;--------------------------------------------------------------------

DisplayFormatCompressed_BaseFormatOffset:

DisplayFormat_ParseCharacters_FromAX:
    mov     si,ax
    ; fall through to DisplayFormat_ParseCharacters

ALIGN JUMP_ALIGN
DisplayFormat_ParseCharacters:
;
; This routine is used to output all strings from the ROM.  The strings in ROMVARS are not compressed,
; and must be handled differently.
;
    cmp     si,byte 07fh        ; well within the boundaries of ROMVARS_size
    mov     bx,cs               ; preload bx with cs in case we take the following jump
    jb      short DisplayPrint_NullTerminatedStringFromBXSI

.decode:
    eSEG    cs
    lodsb                       ; load next byte of the string

    mov     ch,al               ; save a copy for later processing of high order bits

    test    al,0c0h             ; check for translation/format character
    jz      DisplayFormatCompressed_TranslatesAndFormats

    and     al,03fh                             ; "Normal" character, mask off high order bits
    add     al,StringsCompressed_NormalBase     ; and add character offset (usually around 0x40)

.output:
    call    DisplayPrint_CharacterFromAL

.process_after_output:
    shl     ch,1                                ; check high order bits for end of string or space
    jns     short DisplayFormatCompressed_ret
    jnc     .decode
    mov     al,' '
    call    DisplayPrint_CharacterFromAL
    jmp     .decode


ALIGN JUMP_ALIGN
DisplayFormatCompressed_TranslatesAndFormats:
;
; This routine is here (above DisplayFormat_ParseCharacters) to reduce the amount of code between
; DisplayFormatCompressed_BaseFormatOffset and jump targets (must fit in 256 bytes)
;
    shl     ch,1                ; setup ch for later testing of null in .process_after_output
    and     ax,0001fh           ; also clears AH for addition with BX and DX below

    mov     bx,StringsCompressed_TranslatesAndFormats   ; calculate offset of translation/formats offset byte
    add     bx,ax

    cmp     al,StringsCompressed_FormatsBegin           ; determine if this is a translation or a format

    mov     al,[cs:bx]                                  ; fetch translation/formats byte

    jb      DisplayFormat_ParseCharacters.output        ; check if this a translation or a format
                                                        ; if it is translation, output and postprocess for eos
                                                        ; note that the flags for this conditional jump were
                                                        ; set with the cmp al,StringsCompressed_FormatsBegin

    mov     dx,DisplayFormatCompressed_BaseFormatOffset   ; calculate address to jump to for format handler
    sub     dx,ax

    mov     ax,[bp]             ; preload ax with parameter
    dec     bp                  ; if no parameter is needed (format 'nl' for example),
    dec     bp                  ; the format handler can reincrement bp

    mov     bx,0500h            ; preload bh with 5 decimal places for numeric output
                                ; bl is zero, indicating not to output a 'h' (default base 10)

    push    si                  ; preserve si and cx, in the case of outputing a string
    push    cx

    mov     si,10               ; preload si with 10 for numeric output (default base 10)

    call    dx                  ; call the format routine

    pop     cx                  ; restore cx and si
    pop     si

    jmp     DisplayFormat_ParseCharacters.process_after_output  ; continue postprocessing, check for end of string