An unsigned char is a byte; its value can be between 0 and (2^8) - 1 (i.e., 0-255).
for example: unsigned char attach (unsigned char byte, unsigned char bit) { unsigned char mybyte; mybyte = byte&0x7f; if (bit) mybyte |= 0x80; return mybyte; }
unsigned char * memcpy(unsigned char * s1, unsigned char * s2, long size) { long ix; s1= (char *)malloc(sizeof(strlen(s2))); for(ix=0; ix < size; ix++) s1[ix] = s2[ix]; return s1; }
You can find a copy of that file in here: http://ftp.ibiblio.org/pub/micro/PC-stuff/freedos/files/devel/c/dos.h in case the server is down check the extracted file: #ifndef __DOS_H #define __DOS_H #include <_defs.h> #include <stddef.h> #ifdef __WATCOMC__ #pragma pack( __push, 1 ) #endif struct _R16BIT { unsigned short ax, bx, cx, dx, si, di, es, cs, ss, ds, flags; unsigned char cflag; }; struct _R8BIT { unsigned char al, ah, bl, bh, cl, ch, dl, dh; }; union _INTR { struct _R16BIT x; struct _R8BIT h; }; #define INTR _INTR struct country { int co_date; /* date format */ char co_curr[ 5 ]; /* currency symbol */ char co_thsep[ 2 ]; /* thousands separator */ char co_desep[ 2 ]; /* decimal separator */ char co_dtsep[ 2 ]; /* date separator */ char co_tmsep[ 2 ]; /* time separator */ char co_currstyle; /* currency style */ char co_digits; /* significant digits in currency */ char co_time; /* time format */ long co_case; /* case map */ char co_dasep[ 2 ]; /* data separator */ char co_fill[ 10 ]; /* filler */ }; #define COUNTRY country struct DOSERROR { int de_exterror; /* extended error */ char de_class; /* error class */ char de_action; /* action */ char de_locus; /* error locus */ }; struct date { unsigned int da_year; /* current year */ unsigned char da_day; /* day of the month */ unsigned char da_mon; /* month (1 = Jan) */ }; struct dosdate_t { unsigned char day; /* 1--31 */ unsigned char month; /* 1--12 */ unsigned int year; /* 1980--2099 */ unsigned char dayofweek; /* 0--6; 0 = Sunday */ }; struct devhdr { long dh_next; short dh_attr; unsigned short dh_strat; unsigned short dh_inter; char dh_name[ 8 ]; }; struct dfree { unsigned df_avail; /* Available clusters */ unsigned df_total; /* Total clusters */ unsigned df_bsec; /* Bytes per sector */ unsigned df_sclus; /* Sectors per cluster */ }; struct diskfree_t { unsigned total_clusters; unsigned avail_clusters; unsigned sectors_per_cluster; unsigned bytes_per_sector; }; typedef struct { char drive; char pattern [ 13 ]; char reserved [ 7 ]; char attrib; short time; short date; long size; char nameZ [ 13 ]; } dosSearchInfo; struct fatinfo { char fi_sclus; /* sectors per cluster */ char fi_fatid; /* the FAT id byte */ int fi_nclus; /* number of clusters */ int fi_bysec; /* bytes per sector */ }; struct ffblk { #ifdef __CLIB_LFN__ unsigned short cr_time; /* time of file creation */ unsigned short cr_date; /* date of file creation */ unsigned short ac_time; /* time of last file access */ unsigned short ac_date; /* date of last file access */ char ff_reserved[ 13 ]; /* reserved for use by DOS */ #else char ff_reserved[ 21 ]; /* reserved for use by DOS */ #endif char ff_attrib; /* attribute byte for file */ unsigned short ff_ftime; /* time of last write to file */ unsigned short ff_fdate; /* date of last write to file */ unsigned long ff_fsize; /* length of file in bytes */ #ifdef __CLIB_LFN__ char ff_name[ 256 ]; /* null-terminated filename */ unsigned short lfnhandle;/* DOS LFN support handle */ #else char ff_name[ 13 ]; /* null-terminated filename */ #endif }; struct find_t { #ifdef __CLIB_LFN__ unsigned short cr_time; /* time of file creation */ unsigned short cr_date; /* date of file creation */ unsigned short ac_time; /* time of last file access */ unsigned short ac_date; /* date of last file access */ char reserved[ 13 ]; /* reserved for use by DOS */ #else char reserved[ 21 ]; /* reserved for use by DOS */ #endif char attrib; /* attribute byte for file */ unsigned short wr_time; /* time of last write to file */ unsigned short wr_date; /* date of last write to file */ unsigned long size; /* length of file in bytes */ #ifdef __CLIB_LFN__ char name[ 256 ]; /* null-terminated filename */ unsigned short lfnhandle;/* DOS LFN support handle */ #else char name[ 13 ]; /* null-terminated filename */ #endif }; #define _find_t find_t struct fcb { char fcb_drive; char fcb_name[ 8 ], fcb_ext[ 3 ]; short fcb_curblk, fcb_recsize; long fcb_filsize; short fcb_date; char fcb_resv[ 10 ], fcb_currec; long fcb_random; }; struct xfcb { char xfcb_flag; char xfcb_resv[ 5 ]; char xfcb_attr; struct fcb xfcb_fcb; }; struct dostime_t { unsigned char hour; /* Hours */ unsigned char minute; /* Minutes */ unsigned char second; /* Seconds */ unsigned char hsecond; /* Hundredths of seconds */ }; struct time { unsigned char ti_min; /* minutes */ unsigned char ti_hour; /* hours */ unsigned char ti_hund; /* hundredths of seconds */ unsigned char ti_sec; /* seconds */ }; #ifdef __WATCOMC__ #pragma pack( __pop ) #endif extern int __getversion( void ); extern char ** environ; #define _version (*__getversion)() extern unsigned char _osmajor; extern unsigned char _osminor; extern int absread( int drive, int sects, long lsect, void *buffer ); extern int abswrite( int drive, int sects, long lsect, void *buffer ); extern int allocmem( unsigned size, unsigned *seg ); extern int bdos( int ah, unsigned dx, unsigned al ); extern int bdosptr( int ah, void *argument, unsigned al ); extern int _callint( union INTR *regs ); extern struct COUNTRY * country( int xcode, struct COUNTRY *ct ); extern void ctrlbrk( int ( *handler )( void ) ); extern void delay( unsigned mill ); extern void _disable( void ); extern unsigned _dos_allocmem( unsigned size, unsigned *seg ); extern unsigned _dos_close( int handle ); extern unsigned _dos_creat( const char *path, int attr, unsigned *handle ); extern unsigned _dos_creatnew( const char *path, int attr, unsigned *handle ); extern int __cdecl dosexterror( struct DOSERROR *errblk ); extern unsigned _dos_findfirst( char *filename, int attrib, void *strptr ); extern unsigned _dos_findnext( void *strptr ); extern unsigned _dos_findclose( void *strptr ); extern unsigned _dos_freemem( unsigned seg ); extern void __cdecl _dos_getdate( struct dosdate_t *ptr ); extern unsigned __cdecl _dos_getdiskfree( unsigned char dr, struct diskfree_t *d ); extern unsigned _dos_getdrive( unsigned *disk ); extern unsigned _dos_getfileattr( const char *filename, unsigned *attrs ); extern unsigned __cdecl _dos_getftime( int handle, unsigned *date, unsigned *time ); extern void __cdecl _dos_gettime( struct dostime_t *timeptr ); extern void ( interrupt far * _dos_getvect( unsigned intno ) )( ); extern void _dos_keep( unsigned char retcode, unsigned size ); extern unsigned _dos_open( const char *path, unsigned flags, unsigned *handle ); extern unsigned _dos_read( int handle, void far *buf, unsigned len, unsigned *nread ); extern unsigned _dos_setblock( unsigned newsize, unsigned seg, unsigned *max ); extern void _dos_setdate( struct dosdate_t *ptr ); extern void _dos_setdrive( unsigned disk, unsigned *total ); extern unsigned _dos_setfileattr( const char *filename, unsigned attrs ); extern unsigned _dos_setftime( int handle, unsigned date, unsigned time ); extern unsigned _dos_settime( struct dostime_t *timeptr ); extern void _dos_setvect( unsigned intno, void ( interrupt far *vect )() ); extern time_t dostounix( struct date *date, struct time *time ); extern unsigned _dos_write( int handle, void far *buf, unsigned len, unsigned *bytes ); extern void _enable( void ); extern int freemem( unsigned seg ); extern int getcbrk( void ); extern void __cdecl getdate( struct date *datep ); extern void __cdecl getdfree( unsigned char drive, struct dfree *dtable ); extern char * getdta( void ); extern void getfat( unsigned char drive, struct fatinfo *dtable ); extern void getfatd( struct fatinfo *dtable ); extern unsigned getpsp( void ); extern void __cdecl gettime( struct time *timeptr ); extern void ( interrupt far * getvect( int intno ) )( ); extern int getverify( void ); extern int inp( unsigned id ); extern unsigned inpw( unsigned id ); extern unsigned inport( unsigned id ); extern unsigned char inportb( unsigned id ); extern void keep( unsigned char retcode, unsigned size ); extern void nosound( void ); extern int outp( unsigned id, int value ); extern unsigned outpw( unsigned id, unsigned value ); extern void outport( unsigned id, unsigned value ); extern void outportb( unsigned id, unsigned char value ); extern char * parsfnm( const char *cmdline, struct fcb *ptr, int al ); extern int peek( unsigned seg, unsigned offs ); extern char peekb( unsigned seg, unsigned offs ); extern void poke( unsigned seg, unsigned offs, int value ); extern void pokeb( unsigned seg, unsigned offs, char value ); extern int randbrd( struct fcb *buf, int rnum ); extern int randbwr( struct fcb *buf, int rnum ); extern int setblock( unsigned newsize, unsigned seg ); extern int setcbrk( int value ); extern void setdate( struct date *datep ); extern void setdta( char far *dta ); extern void setpsp( unsigned psp ); extern void settime( struct time *timeptr ); extern void setvect( int intno, void ( interrupt far *vect )() ); extern void setverify( int flag ); extern void sleep( unsigned x ); extern void sound( unsigned frequency ); extern void unixtodos( time_t longtime, struct date *date, struct time *time ); extern int unlink( const char *filename ); #define disable _disable #define enable _enable #define _A_NORMAL 0x00 #define _A_RDONLY 0x01 #define _A_HIDDEN 0x02 #define _A_SYSTEM 0x04 #define _A_VOLID 0x08 #define _A_SUBDIR 0x10 #define _A_ARCH 0x20 #define FA_NORMAL _A_NORMAL #define FA_RDONLY _A_RDONLY #define FA_HIDDEN _A_HIDDEN #define FA_SYSTEM _A_SYSTEM #define FA_LABEL _A_VOLID #define FA_DIREC _A_SUBDIR #define FA_ARCH _A_ARCH #define NFDS 20 #define SEEK_SET 0 #define SEEK_CUR 1 #define SEEK_END 2 #define MK_FP( seg, ofs ) ( ( void * )\ ( ( ( unsigned long )( seg ) << 16 ) |\ ( unsigned )( ofs ) ) ) #define FP_SEG(fp) ( ( unsigned )( ( unsigned long )( fp ) >> 16 ) ) #define FP_OFF(fp) ( ( unsigned )( fp ) ) #define __peek( a,b ) ( *( ( int far * ) MK_FP ( ( a ), ( b ) ) ) ) #define __peekb( a,b ) ( *( ( char far * ) MK_FP ( ( a ), ( b ) ) ) ) #define __poke( a,b,c ) ( *( ( int far * ) MK_FP ( (a),(b)) ) = ( int )(c)) #define __pokeb( a,b,c ) ( *( ( char far * ) MK_FP ( (a),(b)) ) = ( char )(c)) #define peek( a,b ) ( *( ( int far * ) MK_FP ( ( a ), ( b ) ) ) ) #define peekb( a,b ) ( *( ( char far * ) MK_FP ( ( a ), ( b ) ) ) ) #define poke( a,b,c ) ( *( ( int far * ) MK_FP ( (a),(b)) ) = ( int )(c)) #define pokeb( a,b,c ) ( *( ( char far * ) MK_FP ( (a),(b)) ) = ( char )(c)) #ifndef __NO_INLINE_FUNCTIONS #pragma aux _enable = "sti"; #pragma aux _disable = "cli"; #pragma aux inp = "in al, dx" parm [dx] value [al] modify [ax dx]; #pragma aux inpw = "in ax, dx" parm [dx] value [ax] modify [ax dx]; #pragma aux inport = "in ax, dx" parm [dx] value [ax] modify [ax dx]; #pragma aux inportb = "in al, dx" parm [dx] value [al] modify [ax dx]; #pragma aux outp = "out dx, al" parm [dx] [al] value [al] modify [ax dx]; #pragma aux outpw = "out dx, ax" parm [dx] [ax] value [ax] modify [ax dx]; #pragma aux outport = "out dx, ax" parm [dx] [ax] modify [ax dx]; #pragma aux outportb = "out dx, al" parm [dx] [al] modify [ax dx]; #endif #endif
What is the significance of declaring a constant unsigned integer?
You can't convert the data type of any variable.
for example: unsigned char attach (unsigned char byte, unsigned char bit) { unsigned char mybyte; mybyte = byte&0x7f; if (bit) mybyte |= 0x80; return mybyte; }
Yes: unsigned char CircLeft (unsigned char value) { if (value&0x80) return (value<<1) + 1; else return (value<<1); } unsigned char CircRight (unsigned char value) { if (value&0x01) return (value>>1) + 0x80; else return (value>>1); }
signed and unsigned
unsigned char * memcpy(unsigned char * s1, unsigned char * s2, long size) { long ix; s1= (char *)malloc(sizeof(strlen(s2))); for(ix=0; ix < size; ix++) s1[ix] = s2[ix]; return s1; }
You can find a copy of that file in here: http://ftp.ibiblio.org/pub/micro/PC-stuff/freedos/files/devel/c/dos.h in case the server is down check the extracted file: #ifndef __DOS_H #define __DOS_H #include <_defs.h> #include <stddef.h> #ifdef __WATCOMC__ #pragma pack( __push, 1 ) #endif struct _R16BIT { unsigned short ax, bx, cx, dx, si, di, es, cs, ss, ds, flags; unsigned char cflag; }; struct _R8BIT { unsigned char al, ah, bl, bh, cl, ch, dl, dh; }; union _INTR { struct _R16BIT x; struct _R8BIT h; }; #define INTR _INTR struct country { int co_date; /* date format */ char co_curr[ 5 ]; /* currency symbol */ char co_thsep[ 2 ]; /* thousands separator */ char co_desep[ 2 ]; /* decimal separator */ char co_dtsep[ 2 ]; /* date separator */ char co_tmsep[ 2 ]; /* time separator */ char co_currstyle; /* currency style */ char co_digits; /* significant digits in currency */ char co_time; /* time format */ long co_case; /* case map */ char co_dasep[ 2 ]; /* data separator */ char co_fill[ 10 ]; /* filler */ }; #define COUNTRY country struct DOSERROR { int de_exterror; /* extended error */ char de_class; /* error class */ char de_action; /* action */ char de_locus; /* error locus */ }; struct date { unsigned int da_year; /* current year */ unsigned char da_day; /* day of the month */ unsigned char da_mon; /* month (1 = Jan) */ }; struct dosdate_t { unsigned char day; /* 1--31 */ unsigned char month; /* 1--12 */ unsigned int year; /* 1980--2099 */ unsigned char dayofweek; /* 0--6; 0 = Sunday */ }; struct devhdr { long dh_next; short dh_attr; unsigned short dh_strat; unsigned short dh_inter; char dh_name[ 8 ]; }; struct dfree { unsigned df_avail; /* Available clusters */ unsigned df_total; /* Total clusters */ unsigned df_bsec; /* Bytes per sector */ unsigned df_sclus; /* Sectors per cluster */ }; struct diskfree_t { unsigned total_clusters; unsigned avail_clusters; unsigned sectors_per_cluster; unsigned bytes_per_sector; }; typedef struct { char drive; char pattern [ 13 ]; char reserved [ 7 ]; char attrib; short time; short date; long size; char nameZ [ 13 ]; } dosSearchInfo; struct fatinfo { char fi_sclus; /* sectors per cluster */ char fi_fatid; /* the FAT id byte */ int fi_nclus; /* number of clusters */ int fi_bysec; /* bytes per sector */ }; struct ffblk { #ifdef __CLIB_LFN__ unsigned short cr_time; /* time of file creation */ unsigned short cr_date; /* date of file creation */ unsigned short ac_time; /* time of last file access */ unsigned short ac_date; /* date of last file access */ char ff_reserved[ 13 ]; /* reserved for use by DOS */ #else char ff_reserved[ 21 ]; /* reserved for use by DOS */ #endif char ff_attrib; /* attribute byte for file */ unsigned short ff_ftime; /* time of last write to file */ unsigned short ff_fdate; /* date of last write to file */ unsigned long ff_fsize; /* length of file in bytes */ #ifdef __CLIB_LFN__ char ff_name[ 256 ]; /* null-terminated filename */ unsigned short lfnhandle;/* DOS LFN support handle */ #else char ff_name[ 13 ]; /* null-terminated filename */ #endif }; struct find_t { #ifdef __CLIB_LFN__ unsigned short cr_time; /* time of file creation */ unsigned short cr_date; /* date of file creation */ unsigned short ac_time; /* time of last file access */ unsigned short ac_date; /* date of last file access */ char reserved[ 13 ]; /* reserved for use by DOS */ #else char reserved[ 21 ]; /* reserved for use by DOS */ #endif char attrib; /* attribute byte for file */ unsigned short wr_time; /* time of last write to file */ unsigned short wr_date; /* date of last write to file */ unsigned long size; /* length of file in bytes */ #ifdef __CLIB_LFN__ char name[ 256 ]; /* null-terminated filename */ unsigned short lfnhandle;/* DOS LFN support handle */ #else char name[ 13 ]; /* null-terminated filename */ #endif }; #define _find_t find_t struct fcb { char fcb_drive; char fcb_name[ 8 ], fcb_ext[ 3 ]; short fcb_curblk, fcb_recsize; long fcb_filsize; short fcb_date; char fcb_resv[ 10 ], fcb_currec; long fcb_random; }; struct xfcb { char xfcb_flag; char xfcb_resv[ 5 ]; char xfcb_attr; struct fcb xfcb_fcb; }; struct dostime_t { unsigned char hour; /* Hours */ unsigned char minute; /* Minutes */ unsigned char second; /* Seconds */ unsigned char hsecond; /* Hundredths of seconds */ }; struct time { unsigned char ti_min; /* minutes */ unsigned char ti_hour; /* hours */ unsigned char ti_hund; /* hundredths of seconds */ unsigned char ti_sec; /* seconds */ }; #ifdef __WATCOMC__ #pragma pack( __pop ) #endif extern int __getversion( void ); extern char ** environ; #define _version (*__getversion)() extern unsigned char _osmajor; extern unsigned char _osminor; extern int absread( int drive, int sects, long lsect, void *buffer ); extern int abswrite( int drive, int sects, long lsect, void *buffer ); extern int allocmem( unsigned size, unsigned *seg ); extern int bdos( int ah, unsigned dx, unsigned al ); extern int bdosptr( int ah, void *argument, unsigned al ); extern int _callint( union INTR *regs ); extern struct COUNTRY * country( int xcode, struct COUNTRY *ct ); extern void ctrlbrk( int ( *handler )( void ) ); extern void delay( unsigned mill ); extern void _disable( void ); extern unsigned _dos_allocmem( unsigned size, unsigned *seg ); extern unsigned _dos_close( int handle ); extern unsigned _dos_creat( const char *path, int attr, unsigned *handle ); extern unsigned _dos_creatnew( const char *path, int attr, unsigned *handle ); extern int __cdecl dosexterror( struct DOSERROR *errblk ); extern unsigned _dos_findfirst( char *filename, int attrib, void *strptr ); extern unsigned _dos_findnext( void *strptr ); extern unsigned _dos_findclose( void *strptr ); extern unsigned _dos_freemem( unsigned seg ); extern void __cdecl _dos_getdate( struct dosdate_t *ptr ); extern unsigned __cdecl _dos_getdiskfree( unsigned char dr, struct diskfree_t *d ); extern unsigned _dos_getdrive( unsigned *disk ); extern unsigned _dos_getfileattr( const char *filename, unsigned *attrs ); extern unsigned __cdecl _dos_getftime( int handle, unsigned *date, unsigned *time ); extern void __cdecl _dos_gettime( struct dostime_t *timeptr ); extern void ( interrupt far * _dos_getvect( unsigned intno ) )( ); extern void _dos_keep( unsigned char retcode, unsigned size ); extern unsigned _dos_open( const char *path, unsigned flags, unsigned *handle ); extern unsigned _dos_read( int handle, void far *buf, unsigned len, unsigned *nread ); extern unsigned _dos_setblock( unsigned newsize, unsigned seg, unsigned *max ); extern void _dos_setdate( struct dosdate_t *ptr ); extern void _dos_setdrive( unsigned disk, unsigned *total ); extern unsigned _dos_setfileattr( const char *filename, unsigned attrs ); extern unsigned _dos_setftime( int handle, unsigned date, unsigned time ); extern unsigned _dos_settime( struct dostime_t *timeptr ); extern void _dos_setvect( unsigned intno, void ( interrupt far *vect )() ); extern time_t dostounix( struct date *date, struct time *time ); extern unsigned _dos_write( int handle, void far *buf, unsigned len, unsigned *bytes ); extern void _enable( void ); extern int freemem( unsigned seg ); extern int getcbrk( void ); extern void __cdecl getdate( struct date *datep ); extern void __cdecl getdfree( unsigned char drive, struct dfree *dtable ); extern char * getdta( void ); extern void getfat( unsigned char drive, struct fatinfo *dtable ); extern void getfatd( struct fatinfo *dtable ); extern unsigned getpsp( void ); extern void __cdecl gettime( struct time *timeptr ); extern void ( interrupt far * getvect( int intno ) )( ); extern int getverify( void ); extern int inp( unsigned id ); extern unsigned inpw( unsigned id ); extern unsigned inport( unsigned id ); extern unsigned char inportb( unsigned id ); extern void keep( unsigned char retcode, unsigned size ); extern void nosound( void ); extern int outp( unsigned id, int value ); extern unsigned outpw( unsigned id, unsigned value ); extern void outport( unsigned id, unsigned value ); extern void outportb( unsigned id, unsigned char value ); extern char * parsfnm( const char *cmdline, struct fcb *ptr, int al ); extern int peek( unsigned seg, unsigned offs ); extern char peekb( unsigned seg, unsigned offs ); extern void poke( unsigned seg, unsigned offs, int value ); extern void pokeb( unsigned seg, unsigned offs, char value ); extern int randbrd( struct fcb *buf, int rnum ); extern int randbwr( struct fcb *buf, int rnum ); extern int setblock( unsigned newsize, unsigned seg ); extern int setcbrk( int value ); extern void setdate( struct date *datep ); extern void setdta( char far *dta ); extern void setpsp( unsigned psp ); extern void settime( struct time *timeptr ); extern void setvect( int intno, void ( interrupt far *vect )() ); extern void setverify( int flag ); extern void sleep( unsigned x ); extern void sound( unsigned frequency ); extern void unixtodos( time_t longtime, struct date *date, struct time *time ); extern int unlink( const char *filename ); #define disable _disable #define enable _enable #define _A_NORMAL 0x00 #define _A_RDONLY 0x01 #define _A_HIDDEN 0x02 #define _A_SYSTEM 0x04 #define _A_VOLID 0x08 #define _A_SUBDIR 0x10 #define _A_ARCH 0x20 #define FA_NORMAL _A_NORMAL #define FA_RDONLY _A_RDONLY #define FA_HIDDEN _A_HIDDEN #define FA_SYSTEM _A_SYSTEM #define FA_LABEL _A_VOLID #define FA_DIREC _A_SUBDIR #define FA_ARCH _A_ARCH #define NFDS 20 #define SEEK_SET 0 #define SEEK_CUR 1 #define SEEK_END 2 #define MK_FP( seg, ofs ) ( ( void * )\ ( ( ( unsigned long )( seg ) << 16 ) |\ ( unsigned )( ofs ) ) ) #define FP_SEG(fp) ( ( unsigned )( ( unsigned long )( fp ) >> 16 ) ) #define FP_OFF(fp) ( ( unsigned )( fp ) ) #define __peek( a,b ) ( *( ( int far * ) MK_FP ( ( a ), ( b ) ) ) ) #define __peekb( a,b ) ( *( ( char far * ) MK_FP ( ( a ), ( b ) ) ) ) #define __poke( a,b,c ) ( *( ( int far * ) MK_FP ( (a),(b)) ) = ( int )(c)) #define __pokeb( a,b,c ) ( *( ( char far * ) MK_FP ( (a),(b)) ) = ( char )(c)) #define peek( a,b ) ( *( ( int far * ) MK_FP ( ( a ), ( b ) ) ) ) #define peekb( a,b ) ( *( ( char far * ) MK_FP ( ( a ), ( b ) ) ) ) #define poke( a,b,c ) ( *( ( int far * ) MK_FP ( (a),(b)) ) = ( int )(c)) #define pokeb( a,b,c ) ( *( ( char far * ) MK_FP ( (a),(b)) ) = ( char )(c)) #ifndef __NO_INLINE_FUNCTIONS #pragma aux _enable = "sti"; #pragma aux _disable = "cli"; #pragma aux inp = "in al, dx" parm [dx] value [al] modify [ax dx]; #pragma aux inpw = "in ax, dx" parm [dx] value [ax] modify [ax dx]; #pragma aux inport = "in ax, dx" parm [dx] value [ax] modify [ax dx]; #pragma aux inportb = "in al, dx" parm [dx] value [al] modify [ax dx]; #pragma aux outp = "out dx, al" parm [dx] [al] value [al] modify [ax dx]; #pragma aux outpw = "out dx, ax" parm [dx] [ax] value [ax] modify [ax dx]; #pragma aux outport = "out dx, ax" parm [dx] [ax] modify [ax dx]; #pragma aux outportb = "out dx, al" parm [dx] [al] modify [ax dx]; #endif #endif
What is the significance of declaring a constant unsigned integer?
You can't convert the data type of any variable.
All possible values of an unsigned char are unsigned, so there is no bit that "represents a signed value." With an 8-bit byte, 1 in the most significant bit of an unsigned char represents the value 128. Consequently unsigned chars with a 1 in this position have values between 128 (when all other bits are 0) and 255 (when all other bits are 1).
unsigned char [16]
The best way I can explain this is to give you an example of code with no documentation. If there was documentation, you would be able to tell what this code did in a matter of seconds. Without it you could waste many minutes, or even hours, trying to understand it. inline unsigned char f_1(const unsigned char *ptr, const unsigned int i) { const div_t d = div(i, 8); return (ptr[d.quot] & (1 << d.rem))?1:0; } inline void f_2(unsigned char *ptr, const unsigned int i) { const div_t d = div(i, 8); ptr += d.quot; *ptr = *ptr | (1 << d.rem); } inline void f_3(unsigned char *ptr, const unsigned int i) { const div_t d = div(i, 8); const unsigned char n = 1 << d.rem; ptr += d.quot; *ptr = ((*ptr | n ) ^ n); } void f(const unsigned int n) { const unsigned int m = n + (n%8==0?0:8-n%8); const unsigned int n = m / 8; const unsigned int m_2 = m / 2; unsigned int i, j; unsigned char *a = malloc(sizeof(unsigned char) * n); memset(a, 0xaa, n); f_3(a, 1); f_2(a, 2); for( i = 3; i < m_2; i+=2 ) { while(i < m_2 && !f_1(a, i)) i+=2; for( j = i + i; j < m; j+=i ) f_3(a, j); } free(a); }
signed char unsigned long int void *
It's their value range:signed char: -128..127unsigned char: 0..255