This function returns ownership of the data structure that contains the current hardware privileged context (the HWPCB) to the operating system and passes ownership of the new HWPCB to the processor.

This function has the following format:

void __PAL_SWPCTX (void *address);

address

A pointer to the new HWPCB.

This function swaps the previous state of the Asynchronous System Trap (AST) enable bit for the new state. The new state is supplied in bit 0 of new_state_mask. The previous state is returned, zero-extended.

A check is made to determine if an AST is pending. If the enabling conditions are present for an AST at the completion of this instruction, the AST occurs before the next instruction.

This function has the following format:

unsigned int __PAL_SWASTEN (int new_state_mask);

new_state_mask

An integer whose 0 bit is the new state of the AST enable bit.

This function writes the low-order three bits of mask into the Processor Status software field (PS<SW>).

This function has the following format:

void __PAL_WR_PS_SW (int mask);

mask

An integer whose low-order three bits are written into PS<SW>.

The _POPCNT built-in function returns the number of "1" bits (0 to 64) in its argument. For example, _POPCNT(12) returns 2.

This function has the following format:

int64 _POPCNT (unsigned int64);

6.2.1.89 _POPPAR

The _POPPAR built-in function returns 1 if the number of "1" bits in its argument is odd; otherwise it returns 0. For example, _POPPAR(12) returns 0.

This function has the following format:

int64 _POPPAR (unsigned int64);

6.2.1.90 Read Process Cycle Counter ( __RPCC)

The __RPCC function reads the current process cycle counter.

This function has the following format:

uint64 __RPCC (void);

6.2.1.91 Sine ( __SIN)

The __SIN built-in is functionally equivalent to its counterpart, sin , in the standard header file <math.h> .

Its format is also the same:

#include <math.h> double __SIN (double x);

x

A radian value.

This built-in offers performance improvements because there is less call overhead associated with its use.

If you include <math.h> , the built-in is automatically used for all occurrences of sin . To disable the built-in, use #undef sin .

6.2.1.92 Single-Precision, Floating-Point Arithmetic Built-in Functions

The following built-in functions provide single-precision, floating-point chopped arithmetic:

__ADDF_C	__ADDS_C	__SUBF_C	__SUBS_C
__MULF_C	__MULS_C	__DIVF_C	__DIVS_C

They have the following format:

float __op{F,S}_C (float operand1, float operand2);

Where op is one of ADD, SUB, MUL, DIV, and {F,S} represents VAX or IEEE floating-point arithmetic, respectively.

The result of the arithmetic operation is returned.

6.2.1.93 Test for Bit Clear then Clear Bit Interlocked (__INTERLOCKED_TESTBITCC_QUAD)

The __INTERLOCKED_TESTBITCC_QUAD function performs the following functions in interlocked fashion:

1. Returns the complement of the specified bit before being cleared.
2. Clears the bit.

This function has one of the following formats:

int __INTERLOCKED_TESTBITCC_QUAD (volatile void *address, int bit_position); int __INTERLOCKED_TESTBITCC_QUAD_RETRY (volatile void *address, int bit_position, int retry, int *status);

address

The quadword-aligned base address of the bit field.

bit_position

The position within the field of the bit that you want cleared, in the range of 0 to 63.

retry

A retry count of type int that indicates the number of times the operation is attempted (which is at least once, even if the retry argument is 0). If the operation cannot be performed successfully in the specified number of retries, the function returns without updating the quadword.

status

A pointer to an integer that is set to 0 if the operation did not succeed within the specified number of retries, and set to 1 if the operation succeeded.

The __TESTBITCCI function performs the following operations in interlocked fashion:

• Returns the complement of the specified bit before being cleared
• Clears the bit

This function has the following format:

int __TESTBITCCI (void *address, int position, ...);

address

The base address of the field.

position

The position within the field of the bit that you want cleared.

...

An optional retry count of type int . If specified, the retry count indicates the number of times the operation is attempted (which will be at least once, even if the count argument is 0).

The __INTERLOCKED_TESTBITSS_QUAD function performs the following functions in interlocked fashion:

1. Returns the value of the specified bit before being set.
2. Sets the bit.

This function has one of the following formats:

int __INTERLOCKED_TESTBITSS_QUAD (volatile void *address, int bit_position); int __INTERLOCKED_TESTBITSS_QUAD_RETRY (volatile void *address, int expression, int retry, int *status);

address

The quadword-aligned base address of the bit field.

bit_position

The position within the field of the bit that you want cleared, in the range of 0 to 63.

retry

A retry count of type int that indicates the number of times the operation is attempted (which is at least once, even if the retry argument is 0). If the operation cannot be performed successfully in the specified number of retries, the function returns without updating the longword.

status

A pointer to an integer that is set to 0 if the operation did not succeed within the specified number of retries, and set to 1 if the operation succeeded.

The __TESTBITSSI function performs the following operations in interlocked fashion:

• Returns the value of the specified bit before being set
• Sets the bit

This function has the following format:

int __TESTBITSSI (void *address, int position, ...);

address

The base address of the field.

position

The position within the field of the bit that you want set.

...

An optional retry count of type int . If specified, the retry count indicates the number of times the operation is attempted (which will be at least once, even if the count argument is 0).

The _TRAILZ built-in function returns the number of trailing zeros (counting after the least significant set bit to the least significant bit position) in its argument. For example, _TRAILZ(2) returns 1, and _TRAILZ(0) returns 64.

This function has the following format:

int64 _TRAILZ (unsigned int64);

6.2.1.98 Trap Barrier Instruction ( __TRAPB)

The __TRAPB function allows software to guarantee that, in a pipeline implementation, all previous arithmetic instructions will be completed without incurring any arithmetic traps before any instructions after the TRAPB instruction are issued.

This function has the following format:

void __TRAPB (void);

6.2.1.99 Unsigned Quadword Multiply High ( __UMULH)

The __UMULH function performs a quadword multiply high instruction.

This function has the following format:

uint64 __UMULH (uint64 operand1, uint64 operand2);

operand1

A 64-bit unsigned integer.

operand2

A 64-bit unsigned integer.

The two operands are multiplied as unsigned integers to produce a 128-bit result. The high-order 64 bits are returned. Note that uint64 is a typedef for the Alpha data type unsigned __int64 .

6.2.2 Built-In Functions for OpenVMS VAX Systems (VAX ONLY)

The following sections describe the Compaq C built-in functions available on OpenVMS VAX systems.

The Compaq C built-in functions use enumerated typedefs to define possible return values. We recommend that you use the enumerated types to store and compare return values.

6.2.2.1 Allocate Bytes from Stack ( __ALLOCA)

The __ALLOCA function allocates n bytes from the stack.

This function has the following format:

void *__ALLOCA (unsigned int n);

n

The number of bytes to be allocated.

A pointer to the allocated memory is returned.

6.2.2.2 Add Aligned Word Interlocked ( _ADAWI)

The _ADAWI function adds its source operand to the destination. This function is interlocked against similar operations by other processors or devices in the system.

The _ADAWI function has the following format:

typedef enum { _adawi_sum_neg=--1, _adawi_sum_zero, _adawi_sum_pos} _ADAWI_STATUS; _ADAWI_STATUS _ADAWI (short __src, short *__dest);

__src

The value to be added to the destination.

__dest

A pointer to the destination. The destination must be aligned on a word boundary. (You can achieve alignment using the _align storage-class modifier.)

There are three possible return values:

• adawi_sum_neg (--1) if the sum when considered to be a signed number is negative
• adawi_sum_zero (0) if the sum is 0
• adawi_sum_pos (1) if the sum is positive

The _BBCCI function performs the following functions in interlocked fashion:

• Returns the complement of the bit specified by the two arguments
• Clears the bit specified by the two arguments

The _BBCCI function has the following format:

typedef enum { _bbcci_oldval_1, _bbcci_oldval_0} _BBCCI_STATUS; _BBCCI_STATUS _BBCCI (int __position, void *__address);

__position

The position of the bit within the field.

__address

The base address of the field.

The return value of _bbcci_oldval_1 (0) or _bbcci_oldval_0 (1) is the complement of the value of the specified bit before being cleared.

6.2.2.4 Branch on Bit Set-Set Interlocked ( _BBSSI)

The _BBSSI function performs the following functions in interlocked fashion:

• Returns the status of the bit specified by the two arguments
• Sets the bit specified by the two arguments

The _BBSSI function has the following format:

typedef enum { _bbssi_oldval_0, _bbcci_oldval_1} _BBSSI_STATUS; _BBSSI_STATUS _BBSSI (int __position, void *__address);

__position

The position of the bit within the field.

__address

The base address of the field.

The return value of _bbssi_oldval_0 (0) or _bbssi_oldval_1 (1) is the value of the specified bit before being set.

6.2.2.5 Find First Clear Bit ( _FFC)

The _FFC function finds the position of the first clear bit in a field. The bits are tested for clear status starting at bit 0 and extending to the highest bit in the field.

The _FFC function has the following format:

typedef enum { _ff_bit_not_found, _ff_bit_found} _FF_STATUS; _FF_STATUS _FFC (int __start, char __size, const void *__base, int *__position);

__start

The start position of the field.

__size

The size of the field, in bits. The size must be a value from 0 to 32 bits.

__base

The address of the field.

__position

The address of an integer to receive the position of the clear bit. If no bit is clear, the integer is set to the position of the first bit past the last bit tested.

There are two possible return values:

• _ff_bit_not_found (0) if all bits in the field are set
• _ff_bit_found (1) if a bit with value 0 is found

The _FFS function finds the position of the first set bit in a field. The bits are tested for set status starting at bit 0 and extending to the highest bit in the field.

The _FFS function has the following format:

typedef enum { _ff_bit_not_found, _ff_bit_found} _FF_STATUS; _FF_STATUS _FFS (int __start, char __size, const void *__base, int *__position);

__start

The start position of the field.

__size

The size of the field, in bits. The size must be a value from 0 to 32 bits.

__base

The address of the field.

__position

The address of an integer to receive the position of the set bit. If no bit is set, the integer is set to the position of the first bit past the last bit tested.

There are two possible return values:

• _ff_bit_not_found (0) if all bits in the field are clear
• _ff_bit_found (1) if a bit with value 1 is found

The _HALT function halts the processor when executed by a process running in kernel mode. This is a privileged function.

The _HALT function has the following format:

void _HALT (void);

6.2.2.8 Insert Entry into Queue at Head Interlocked ( _INSQHI)

The _INSQHI function inserts an entry into the front of a queue in an indivisible manner. This operation is interlocked against similar operations by other processors or devices in the system.

The _INSQHI function has the following format:

typedef enum {_insqi_inserted_many, _insqi_not_inserted, _insqi_inserted_only} _INSQI_STATUS; _INSQI_STATUS _INSQHI (void *__new_entry, void *__head);

__new_entry

A pointer to the new entry to be inserted. The entry must be aligned on a quadword boundary. (You can achieve alignment using the _align storage-class modifier.)

__head

A pointer to the queue header. The header must be aligned on a quadword boundary. (You can achieve alignment using the _align storage-class modifier.)

There are three possible return values:

• _insqi_inserted_many (0) if the entry was inserted, but it was not the only entry in the list
• _insqi_not_inserted (1) if the entry was not inserted because the secondary interlock failed
• _insqi_inserted_only (2) if the entry was inserted and it was the only entry in the list

The _INSQTI function inserts an entry at the end of a queue in an indivisible manner. This operation is interlocked against similar operations by other processors or devices in the system.

The _INSQTI function has the following format:

typedef enum {_insqi_inserted_many, _insqi_not_inserted, _insqi_inserted_only} _INSQI_STATUS; _INSQI_STATUS _INSQTI (void *__new_entry, void *__head);

__new_entry

A pointer to the new entry to be inserted. The entry must be aligned on a quadword boundary. (You can achieve alignment using the _align storage-class modifier.)

__head

A pointer to the queue header. The header must be aligned on a quadword boundary. (You can achieve alignment using the _align storage-class modifier.)

There are three possible return values:

• _insqi_inserted_many (0) if the entry was inserted, but it was not the only entry in the list
• _insqi_not_inserted (1) if the entry was not inserted because the secondary interlock failed
• _insqi_inserted_only (2) if the entry was inserted and it was the only entry in the list

The _INSQUE function inserts a new entry into a queue following an existing entry.

The _INSQUE function has the following format:

typedef enum { _insque_inserted_only, _insque_inserted_many} _INSQUE_STATUS; _INSQUE_STATUS _INSQUE (void *__new_entry, void *__predecessor);

__new_entry

A pointer to the new entry to be inserted.

__predecessor

A pointer to an existing entry in the queue.

There are two possible return values:

• _insque_inserted_only (0) if the entry was the only entry in the queue
• _insque_inserted_many (1) if the entry was not the only entry in the queue

privacy and legal statement