Humble Framework for SkyOS

projects / Humble

HAL.h File Reference

Detailed Description

This is the "Hardware Abstraction Layer" (HAL), which is intended to make porting code easier by added a thin layer of predefined constants and primitive data types that can be quickly tailored to different environments. Rather than wondering whether an int variable is 16 bits or 32 bits wide, the HAL defines things like int16 and int32 (as well as uint16 and uint32 for unsigned versions) which makes the code pretty obvious. The HAL also helps overcome some minor variations in RTL function names—such as strcmpi() vs. stricmp()—by wrapping common run-time library calls. None of this makes the resulting application any faster or smaller, but it does make the code a bit more readable; it also makes it a bit more robust by helping prevent some of the more common programming errors.

Definition in file HAL.h.

Go to the source code of this file.

Namespaces

namespace Humble

Defines

#define TEXT(p)   ((unsigned char *)(p))

#define NOTHING   ((void)0)

#define KB(n)   ((n) * 1024)

#define MB(n)   (KB(n) * 1024)

#define GB(n)   (MB(n) * 1024)

#define ARRAY_DIM(x)   (sizeof(x)/sizeof((x)[0]))

Computes the number of elements in an array.

#define GOOD_HND(h)   (NULL != HANDLE(h))

Evaluates to true if a handle is valid.

#define NULL_HND(h)   (NULL == HANDLE(h))

Evalutes to true if a handle is NOT valid.

#define GOOD_PTR(p)   (NULL != Ptr(p))

Evaluates to true if a pointer is valid.

#define NULL_PTR(p)   (NULL == Ptr(p))

Evaluates to true if a pointer is NOT valid.

#define MAKE_PTR(c, p, n)   reinterpret_cast<c>(size_t(p)+size_t(n))

#define GCC_ONLY(x)

#define TEST_ONLY(x)

#define MEM_CMP(x, y, n)   Humble::safe_memcmp((x),(y),(n))

#define MEM_COPY(d, s, n)   Humble::safe_memcpy((d),(s),(n))

Portable alias for the "memory copy" RTL function (memcpy).

#define MEM_FILL(d, c, n)   Humble::safe_memset((d),(c),(n))

Portable alias for the "memory set" RTL function (memset).

#define MEM_MOVE(d, s, n)   Humble::safe_memmove((d),(s),(n))

Portable alias for the "memory move" RTL function (memmove).

#define MEM_ZERO(d, n)   Humble::safe_memset((d),0x00,(n))

Portable alias for the "memory zero" RTL function.

#define STR_COUNT(p, c)   Humble::safe_strcount((p),(c))

#define STR_EMPTY(p)   (NULL_PTR(p) || *(p) == '\0')

Evaluates to true if a pointer is invalid, or references a zero-length string.

#define STR_SAFE(p)   (GOOD_PTR(p) ? (p) : kStrEmpty)

Returns a string, or an empty string ("") if the string pointer is invalid.

#define STR_VALID(p)   (GOOD_PTR(p) && *(p) != '\0')

Evaluates to true if a string is valid and non-empty (opposite to STR_EMPTY).

#define STR_CAT(s, d, n)   Humble::safe_strncat((s),(d),(n))

Substitute for the "string character search" (strncat) RTL function.

#define STR_CHR(s, c)   Humble::safe_strchr((s),(c))

Substitute for the "string character search" (strchr) RTL function.

#define STR_CMP(a, b)   Humble::safe_strcmp((a),(b))

Substitue for the "string compare" (strcmp) RTL function.

#define STR_ICMP(a, b)   Humble::safe_strcmpi((a),(b))

Substitue for the "string case insensitive compare" (stricmp) RTL function.

#define STR_NCMP(a, b, n)   Humble::safe_strcmpn((a),(b),(n))

Substitue for the "string case fixed length compare" (strncmp) RTL function.

#define STR_WCMP(a, b)   Humble::safe_strcmpw((a),(b))

string case wildcard compare" function

#define STR_CPY(s, d)   Humble::safe_strncpy((s),(d))

Substitue for the "string copy" (strnpy) RTL function.

#define STR_NCPY(s, d, n)   Humble::safe_strncpy((s),(d),(n))

#define STR_LEN(s)   Humble::safe_strlen(s)

Substitue for the "string length" (strlen) RTL function.

#define STR_NLEN(s, u)   Humble::safe_strlen((s),(u))

#define STR_LWR(s)   Humble::safe_strlwr(s)

Substitue for the "string lower" (strlwr) RTL function.

#define STR_RCHR(s, c)   Humble::safe_strrchr((s),(c))

Substitute for the "string reverse character search" (strrchr) RTL function.

#define STR_REV(s)   Humble::safe_strrev(s)

Substitute for the "string reverse" (strrev) RTL function.

#define STR_SPRINTF   Humble::safe_sprintf

Portable alias for the "string formatting" RTL function (sprintf).

#define STR_STR(s, a)   Humble::safe_strstr((s),(a))

Substitute for the "string substring search" (strstr) RTL function.

#define STR_TO_INT(s)   Humble::safe_strtoi(s)

Substitute for the "string to integer" (strtoi) RTL function.

#define STR_UPR(s)   Humble::safe_strupr(s)

Substitue for the "string upper" (strupr) RTL function.

#define STR_VSPRINTF   Humble::safe_vsprintf

Portable alias for the vsprintf() RTL function.

Typedefs

typedef char Text

< Portable alias for a single character (char) Portable alias for a character (string) pointer (char *)

typedef Text * TextPtr

Portable alias for a pointer to a constant string (char const *).

typedef Text const * StringPtr

typedef signed char int8

< Portable alias for a signed 8-bit value Portable alias for an unsigned 8-bit value

typedef unsigned char uint8

typedef short int16

< Portable alias for a signed 15-bit value Portable alias for an unsigned 15-bit value

typedef unsigned short uint16

typedef long int32

< Portable alias for a signed 32-bit value Portable alias for an unsigned 32-bit value

typedef unsigned long uint32

typedef void * Ptr

< Portable alias for a void pointer (void *) Portable alias for a pointer to constant byte data (const unsigned char *)

typedef void const * PtrConst

Portable alias for a pointer to byte data (unsigned char *).

typedef uint8 * PtrData

Portable alias for a pointer to byte data (unsigned char *).

typedef uint8 const * PtrDataConst

Force a string as changeable to avoid compiler warnings.

Functions

template<class T>

T max (const T &x, const T &y)

Returns the greater of two values.

template<class T>

T min (const T &x, const T &y)

Returns the lesser of two values.

template<class T>

void minmax (const T *array, uint32 uCount, T &minVal, T &maxVal)

Find the min/max of an array.

template<class T>

void swap (T &x, T &y)

A generic swap() function.

template<class T>

void swapInPlace (T &x, T &y)

A generic swap() function that does not create a temporary object.

void PopUpAlert (StringPtr, StringPtr pstrBase=NULL,...)

Displays the prompt dialog and waits for the user to acknowledge it.

void PopUpInfo (StringPtr, StringPtr pstrBase=NULL,...)

Displays the prompt dialog and waits for the user to acknowledge it.

int32 PopUpOKCancel (StringPtr, StringPtr pstrBase=NULL,...)

Displays the prompt dialog and waits for the user to acknowledge it.

int32 PopUpYesNo (StringPtr, StringPtr pstrBase=NULL,...)

Displays the prompt dialog and waits for the user to acknowledge it.

int32 safe_memcmp (PtrConst, PtrConst, uint32)

Replacement for the "memory comparison" (memcmp) RTL function.

Ptr safe_memcpy (Ptr, PtrConst, uint32)

Replacement for the "memory copy" (memcpy) RTL function.

Ptr safe_memmove (Ptr, PtrConst, uint32)

Replacement for the "memory move" (memmove) RTL function.

Ptr safe_memset (Ptr, uint8, uint32)

Replacement for the "memory set" (memset) RTL function.

StringPtr safe_strchr (StringPtr, Text)

Replacement for the "string character" (strchr) RTL function.

int32 safe_strcmp (StringPtr, StringPtr)

Replacement for the "string comparison" (strcmp) RTL function.

int32 safe_strcmpi (StringPtr, StringPtr)

Replacement for the "string comparison" (stricmp) RTL function.

int32 safe_strcmpn (StringPtr, StringPtr, uint32)

Replacement for the "string comparison" (strncmp) RTL function.

bool safe_strcmpw (StringPtr, StringPtr)

String comparison function with wildcards.

TextPtr safe_strncat (TextPtr, StringPtr, int32)

Replacement for the "string concatenate" (strncat) RTL function.

TextPtr safe_strncpy (TextPtr, StringPtr, int32 nMaxLen=INT32_MAX)

Replacement for the "string copy" (strncpy) RTL function.

int32 safe_strcount (StringPtr, Text)

Counts the number of times a character is found in a string.

int safe_strlen (StringPtr, int32 nMaxLen=INT32_MAX)

Replacement for the "string length" (strlen) RTL function.

TextPtr safe_strlwr (TextPtr)

Replacement for the "string lower" (strlwr) RTL function.

StringPtr safe_strrchr (StringPtr, Text)

Replacement for the "string reverse character" (strrchr) RTL function.

TextPtr safe_strrev (TextPtr)

Replacement for the "string reverse" (strrev) RTL function.

StringPtr safe_strstr (StringPtr, StringPtr)

Replacement for the "string substring search" (strstr) RTL function.

int32 safe_strtoi (StringPtr)

Converts a string to an integer.

TextPtr safe_strupr (TextPtr)

Replacement for the "string upper" (strupr) RTL function.

int32 safe_vsprintf (TextPtr, int32, StringPtr, va_list)

Replacement for the vsprintf() RTL function.

int32 safe_sprintf (TextPtr, int32, StringPtr,...)

Replacement for the sprintf() RTL function.

Variables

const int8 INT8_MAX = SCHAR_MAX

maximum value for int8

const int8 INT8_MIN = SCHAR_MIN

minimum value for int8

const uint8 UINT8_MAX = UCHAR_MAX

maximum value for uint8

const int16 INT16_MAX = SHRT_MAX

maximum value for int16

const int16 INT16_MIN = SHRT_MIN

minimum value for int16

const uint16 UINT16_MAX = USHRT_MAX

maximum value for uint16

const int32 INT32_MAX = LONG_MAX

maximum value for int32

const int32 INT32_MIN = LONG_MIN

minimum value for int32

const uint32 UINT32_MAX = ULONG_MAX

maximum value for uint32

const StringPtr kStrEmpty = ""

An empty string.

const StringPtr kStrEOL = "\n"

An End of Line string.

const Text kDirSeparator = '/'

The character used to separate directories in a file path.

const uint32 MAX_PATH = 1023

Maximum length of a fully-qualified file specifier (4096 according to API?).

const HRESULT S_FAILED = ~S_OK

const uint32 BAD_INDEX = std::string::npos

Function Documentation

template<class T>

T Humble::max ( const T & x,

const T & y

)

Returns:
Larger of x and y

Parameters:

x First value

y Second value

Definition at line 238 of file HAL.h.

template<class T>

T Humble::min ( const T & x,

const T & y

)

Returns:
Smaller of x and y

Parameters:

x First value

y Second value

Definition at line 249 of file HAL.h.

template<class T>

void Humble::minmax ( const T * array,

uint32 uCount,

T & minVal,

T & maxVal

)

This procedure computes minimum min and maximum max of n numbers using only (3n / 2) - 2 comparisons.

Parameters:

array Ptr to base of array

uCount Count of array elements

[out] minVal Minimum value found

[out] maxVal Maximum value found

Definition at line 264 of file HAL.h.

template<class T>

void Humble::swap ( T & x,

T & y

)

This function will swap the values of two variable, providing they are identical data types. (Note: Classes declared with the HObjNoCopy mix- in class cannot be "swapped". This is by design.)

Parameters:

x first variable to be exchanged

y second variable to be exchanged

Definition at line 313 of file HAL.h.

template<class T>

void Humble::swapInPlace ( T & x,

T & y

)

This function will swap the values of two variable, providing they are identical data types. The items are swapped "in line" using XOR operations to avoid the need to create a temporary object. This is useful for data types that are very large.

Parameters:

x first variable to be exchanged

y second variable to be exchanged

Definition at line 328 of file HAL.h.

void Humble::PopUpAlert ( StringPtr pstrTitle,

StringPtr pstrBase,

...

)

Allows printf-style arguments to be passed in.

Returns:
User's selection (ID_OK, ID_CANCEL, ID_YES, etc.)

Parameters:

pstrTitle Caption of dialog box

pstrBase Message to display

See also:
PopUpInfo()

Definition at line 815 of file Humble.cpp.

void Humble::PopUpInfo ( StringPtr pstrTitle,

StringPtr pstrBase,

...

)

Allows printf-style arguments to be passed in.

Returns:
User's selection (ID_OK, ID_CANCEL, ID_YES, etc.)

Parameters:

pstrTitle Caption of dialog box

pstrBase Message to display

See also:
PopUpAlert()

Definition at line 845 of file Humble.cpp.

int32 Humble::PopUpOKCancel ( StringPtr pstrTitle,

StringPtr pstrBase,

...

)

Allows printf-style arguments to be passed in.

Returns:
User's selection (ID_OK, ID_CANCEL, ID_YES, etc.)

Parameters:

pstrTitle Caption of dialog box

pstrBase Message to display

See also:
PopUpYesNo()

Definition at line 875 of file Humble.cpp.

int32 Humble::PopUpYesNo ( StringPtr pstrTitle,

StringPtr pstrBase,

...

)

Allows printf-style arguments to be passed in.

Returns:
User's selection (ID_OK, ID_CANCEL, ID_YES, etc.)

Parameters:

pstrTitle Caption of dialog box

pstrBase Message to display

See also:
PopUpOKCancel()

Definition at line 910 of file Humble.cpp.

int32 Humble::safe_strcmpn ( StringPtr pstr1,

StringPtr pstr2,

uint32 uMaxLen

)

This method is identical to strncmp(), but is also guaranteed to correctly handle NULL parameters. This method is wrapped by the STR_CMPN macro.

Returns:
Zero if the two strings are equal,

Parameters:

pstr1 Left string to compare

pstr2 Right string to compare

uMaxLen Maximum length of stringto compare

See also:
STR_CMPN

Definition at line 370 of file Humble.cpp.

TextPtr Humble::safe_strncpy ( TextPtr pszDst,

StringPtr pstrSrc,

int32 nMaxLen

)

This method is identical to strncpy(), but is also guaranteed to correctly handle NULL parameters. This method is wrapped by the STR_CPY and STR_NCPY macros.

Returns:
Destination string after copy

Parameters:

pszDst Source string

pstrSrc Destination string

nMaxLen Maximum length of destination string

See also:
STR_CPY
STR_NCPY

Definition at line 515 of file Humble.cpp.


Namespaces
namespace	Humble
Defines
#define	TEXT(p) ((unsigned char *)(p))
#define	NOTHING ((void)0)
#define	KB(n) ((n) * 1024)
#define	MB(n) (KB(n) * 1024)
#define	GB(n) (MB(n) * 1024)
#define	ARRAY_DIM(x) (sizeof(x)/sizeof((x)[0]))
	Computes the number of elements in an array.
#define	GOOD_HND(h) (NULL != HANDLE(h))
	Evaluates to true if a handle is valid.
#define	NULL_HND(h) (NULL == HANDLE(h))
	Evalutes to true if a handle is NOT valid.
#define	GOOD_PTR(p) (NULL != Ptr(p))
	Evaluates to true if a pointer is valid.
#define	NULL_PTR(p) (NULL == Ptr(p))
	Evaluates to true if a pointer is NOT valid.
#define	MAKE_PTR(c, p, n) reinterpret_cast<c>(size_t(p)+size_t(n))
#define	GCC_ONLY(x)
#define	TEST_ONLY(x)
#define	MEM_CMP(x, y, n) Humble::safe_memcmp((x),(y),(n))
#define	MEM_COPY(d, s, n) Humble::safe_memcpy((d),(s),(n))
	Portable alias for the "memory copy" RTL function (memcpy).
#define	MEM_FILL(d, c, n) Humble::safe_memset((d),(c),(n))
	Portable alias for the "memory set" RTL function (memset).
#define	MEM_MOVE(d, s, n) Humble::safe_memmove((d),(s),(n))
	Portable alias for the "memory move" RTL function (memmove).
#define	MEM_ZERO(d, n) Humble::safe_memset((d),0x00,(n))
	Portable alias for the "memory zero" RTL function.
#define	STR_COUNT(p, c) Humble::safe_strcount((p),(c))
#define	STR_EMPTY(p) (NULL_PTR(p) \|\| *(p) == '\0')
	Evaluates to true if a pointer is invalid, or references a zero-length string.
#define	STR_SAFE(p) (GOOD_PTR(p) ? (p) : kStrEmpty)
	Returns a string, or an empty string ("") if the string pointer is invalid.
#define	STR_VALID(p) (GOOD_PTR(p) && *(p) != '\0')
	Evaluates to true if a string is valid and non-empty (opposite to STR_EMPTY).
#define	STR_CAT(s, d, n) Humble::safe_strncat((s),(d),(n))
	Substitute for the "string character search" (strncat) RTL function.
#define	STR_CHR(s, c) Humble::safe_strchr((s),(c))
	Substitute for the "string character search" (strchr) RTL function.
#define	STR_CMP(a, b) Humble::safe_strcmp((a),(b))
	Substitue for the "string compare" (strcmp) RTL function.
#define	STR_ICMP(a, b) Humble::safe_strcmpi((a),(b))
	Substitue for the "string case insensitive compare" (stricmp) RTL function.
#define	STR_NCMP(a, b, n) Humble::safe_strcmpn((a),(b),(n))
	Substitue for the "string case fixed length compare" (strncmp) RTL function.
#define	STR_WCMP(a, b) Humble::safe_strcmpw((a),(b))
	string case wildcard compare" function
#define	STR_CPY(s, d) Humble::safe_strncpy((s),(d))
	Substitue for the "string copy" (strnpy) RTL function.
#define	STR_NCPY(s, d, n) Humble::safe_strncpy((s),(d),(n))
#define	STR_LEN(s) Humble::safe_strlen(s)
	Substitue for the "string length" (strlen) RTL function.
#define	STR_NLEN(s, u) Humble::safe_strlen((s),(u))
#define	STR_LWR(s) Humble::safe_strlwr(s)
	Substitue for the "string lower" (strlwr) RTL function.
#define	STR_RCHR(s, c) Humble::safe_strrchr((s),(c))
	Substitute for the "string reverse character search" (strrchr) RTL function.
#define	STR_REV(s) Humble::safe_strrev(s)
	Substitute for the "string reverse" (strrev) RTL function.
#define	STR_SPRINTF Humble::safe_sprintf
	Portable alias for the "string formatting" RTL function (sprintf).
#define	STR_STR(s, a) Humble::safe_strstr((s),(a))
	Substitute for the "string substring search" (strstr) RTL function.
#define	STR_TO_INT(s) Humble::safe_strtoi(s)
	Substitute for the "string to integer" (strtoi) RTL function.
#define	STR_UPR(s) Humble::safe_strupr(s)
	Substitue for the "string upper" (strupr) RTL function.
#define	STR_VSPRINTF Humble::safe_vsprintf
	Portable alias for the vsprintf() RTL function.
Typedefs
typedef char	Text
	< Portable alias for a single character (char) Portable alias for a character (string) pointer (char *)
typedef Text *	TextPtr
	Portable alias for a pointer to a constant string (char const *).
typedef Text const *	StringPtr
typedef signed char	int8
	< Portable alias for a signed 8-bit value Portable alias for an unsigned 8-bit value
typedef unsigned char	uint8
typedef short	int16
	< Portable alias for a signed 15-bit value Portable alias for an unsigned 15-bit value
typedef unsigned short	uint16
typedef long	int32
	< Portable alias for a signed 32-bit value Portable alias for an unsigned 32-bit value
typedef unsigned long	uint32
typedef void *	Ptr
	< Portable alias for a void pointer (void ) Portable alias for a pointer to constant byte data (const unsigned char )
typedef void const *	PtrConst
	Portable alias for a pointer to byte data (unsigned char *).
typedef uint8 *	PtrData
	Portable alias for a pointer to byte data (unsigned char *).
typedef uint8 const *	PtrDataConst
	Force a string as changeable to avoid compiler warnings.
Functions
template<class T>
T	max (const T &x, const T &y)
	Returns the greater of two values.
template<class T>
T	min (const T &x, const T &y)
	Returns the lesser of two values.
template<class T>
void	minmax (const T *array, uint32 uCount, T &minVal, T &maxVal)
	Find the min/max of an array.
template<class T>
void	swap (T &x, T &y)
	A generic swap() function.
template<class T>
void	swapInPlace (T &x, T &y)
	A generic swap() function that does not create a temporary object.
void	PopUpAlert (StringPtr, StringPtr pstrBase=NULL,...)
	Displays the prompt dialog and waits for the user to acknowledge it.
void	PopUpInfo (StringPtr, StringPtr pstrBase=NULL,...)
	Displays the prompt dialog and waits for the user to acknowledge it.
int32	PopUpOKCancel (StringPtr, StringPtr pstrBase=NULL,...)
	Displays the prompt dialog and waits for the user to acknowledge it.
int32	PopUpYesNo (StringPtr, StringPtr pstrBase=NULL,...)
	Displays the prompt dialog and waits for the user to acknowledge it.
int32	safe_memcmp (PtrConst, PtrConst, uint32)
	Replacement for the "memory comparison" (memcmp) RTL function.
Ptr	safe_memcpy (Ptr, PtrConst, uint32)
	Replacement for the "memory copy" (memcpy) RTL function.
Ptr	safe_memmove (Ptr, PtrConst, uint32)
	Replacement for the "memory move" (memmove) RTL function.
Ptr	safe_memset (Ptr, uint8, uint32)
	Replacement for the "memory set" (memset) RTL function.
StringPtr	safe_strchr (StringPtr, Text)
	Replacement for the "string character" (strchr) RTL function.
int32	safe_strcmp (StringPtr, StringPtr)
	Replacement for the "string comparison" (strcmp) RTL function.
int32	safe_strcmpi (StringPtr, StringPtr)
	Replacement for the "string comparison" (stricmp) RTL function.
int32	safe_strcmpn (StringPtr, StringPtr, uint32)
	Replacement for the "string comparison" (strncmp) RTL function.
bool	safe_strcmpw (StringPtr, StringPtr)
	String comparison function with wildcards.
TextPtr	safe_strncat (TextPtr, StringPtr, int32)
	Replacement for the "string concatenate" (strncat) RTL function.
TextPtr	safe_strncpy (TextPtr, StringPtr, int32 nMaxLen=INT32_MAX)
	Replacement for the "string copy" (strncpy) RTL function.
int32	safe_strcount (StringPtr, Text)
	Counts the number of times a character is found in a string.
int	safe_strlen (StringPtr, int32 nMaxLen=INT32_MAX)
	Replacement for the "string length" (strlen) RTL function.
TextPtr	safe_strlwr (TextPtr)
	Replacement for the "string lower" (strlwr) RTL function.
StringPtr	safe_strrchr (StringPtr, Text)
	Replacement for the "string reverse character" (strrchr) RTL function.
TextPtr	safe_strrev (TextPtr)
	Replacement for the "string reverse" (strrev) RTL function.
StringPtr	safe_strstr (StringPtr, StringPtr)
	Replacement for the "string substring search" (strstr) RTL function.
int32	safe_strtoi (StringPtr)
	Converts a string to an integer.
TextPtr	safe_strupr (TextPtr)
	Replacement for the "string upper" (strupr) RTL function.
int32	safe_vsprintf (TextPtr, int32, StringPtr, va_list)
	Replacement for the vsprintf() RTL function.
int32	safe_sprintf (TextPtr, int32, StringPtr,...)
	Replacement for the sprintf() RTL function.
Variables
const int8	INT8_MAX = SCHAR_MAX
	maximum value for int8
const int8	INT8_MIN = SCHAR_MIN
	minimum value for int8
const uint8	UINT8_MAX = UCHAR_MAX
	maximum value for uint8
const int16	INT16_MAX = SHRT_MAX
	maximum value for int16
const int16	INT16_MIN = SHRT_MIN
	minimum value for int16
const uint16	UINT16_MAX = USHRT_MAX
	maximum value for uint16
const int32	INT32_MAX = LONG_MAX
	maximum value for int32
const int32	INT32_MIN = LONG_MIN
	minimum value for int32
const uint32	UINT32_MAX = ULONG_MAX
	maximum value for uint32
const StringPtr	kStrEmpty = ""
	An empty string.
const StringPtr	kStrEOL = "\n"
	An End of Line string.
const Text	kDirSeparator = '/'
	The character used to separate directories in a file path.
const uint32	MAX_PATH = 1023
	Maximum length of a fully-qualified file specifier (4096 according to API?).
const HRESULT	S_FAILED = ~S_OK
const uint32	BAD_INDEX = std::string::npos