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// TITLE("Interlocked Increment and Decrement Support")//++//// Copyright (c) 1991 Microsoft Corporation// Copyright (c) 1992 Digital Equipment Corporation//// Module Name://// critsect.s//// Abstract://// This module implements functions to support user mode critical sections.// It contains some code from ntos\dll\alpha\critsect.s but without the Rtl// prefix.//// Author://// David N. Cutler 29-Apr-1992//// Environment://// Any mode.//// Revision History://// Thomas Van Baak (tvb) 22-Jul-1992//// Adapted for Alpha AXP.////--
#include "ksalpha.h"
SBTTL("Interlocked Increment")//++//// LONG// InterlockedIncrement(// IN PLONG Addend// )//// Routine Description://// This function performs an interlocked increment on the addend variable.//// This function and its companion are assuming that the count will never// be incremented past 2**31 - 1.//// Arguments://// Addend (a0) - Supplies a pointer to a variable whose value is to be// incremented.//// Return Value://// A negative value is returned if the updated value is less than zero,// a zero value is returned if the updated value is zero, and a nonzero// positive value is returned if the updated value is greater than zero.////--
LEAF_ENTRY(InterlockedIncrement)
10: mb // synchronize memory access ldl_l v0, 0(a0) // get addend value - locked addl v0, 1, v0 // increment addend value mov v0, t0 // copy updated value to t0 for store stl_c t0, 0(a0) // store conditionally beq t0, 20f // if eq, conditional store failed mb // synchronize memory access ret zero, (ra) // return
//// We expect the store conditional will usually succeed the first time so it// is faster to branch forward (predicted not taken) to here and then branch// backward (predicted taken) to where we wanted to go.//
20: br zero, 10b // go try load again
.end InterlockedIncrement SBTTL("InterlockedDecrement")//++//// LONG// InterlockedDecrement(// IN PLONG Addend// )//// Routine Description://// This function performs an interlocked decrement on the addend variable.//// This function and its companion are assuming that the count will never// be decremented past 2**31 - 1.//// Arguments://// Addend (a0) - Supplies a pointer to a variable whose value is to be// decremented.//// Return Value://// A negative value is returned if the updated value is less than zero,// a zero value is returned if the updated value is zero, and a nonzero// positive value is returned if the updated value is greater than zero.////--
LEAF_ENTRY(InterlockedDecrement)
10: mb // synchronize memory access ldl_l v0, 0(a0) // get addend value - locked subl v0, 1, v0 // decrement addend value mov v0, t0 // copy updated value to t0 for store stl_c t0, 0(a0) // store conditionally beq t0, 20f // if eq, conditional store failed mb // synchronize memory access ret zero, (ra) // return
//// We expect the store conditional will usually succeed the first time so it// is faster to branch forward (predicted not taken) to here and then branch// backward (predicted taken) to where we wanted to go.//
20: br zero, 10b // go try load again
.end InterlockedDecrement SBTTL("Interlocked Exchange")//++//// ULONG// InterlockedExchange (// IN PULONG Source,// IN ULONG Value// )//// Routine Description://// This function performs an interlocked exchange of a longword value with// a longword in memory and returns the memory value.//// Arguments://// Source (a0) - Supplies a pointer to a variable whose value is to be// exchanged.//// Value (a1) - Supplies the value to exchange with the source value.//// Return Value://// The source value is returned as the function value.////--
LEAF_ENTRY(InterlockedExchange)
10: mb // synchronize memory access ldl_l v0,0(a0) // get current source value xor a1,zero,t0 // set exchange value stl_c t0,0(a0) // replace source value beq t0,20f // if eq, conditional store failed mb // synchronize memory access ret zero,(ra) // else/ return old value to caller
//// We expect the store conditional will usually succeed the first time so it// is faster to branch forward (predicted not taken) to here and then branch// backward (predicted taken) to where we wanted to go.//
20: br zero,10b // go try spin lock again
.end InterlockedExchange SBTTL("Interlocked Compare Exchange")//++//// LONG// InterlockedCompareExchange (// IN OUT PLONG *Destination,// IN LONG Exchange,// IN LONG Comperand// )//// Routine Description://// This function performs an interlocked compare of the destination// value with the comperand value. If the destination value is equal// to the comperand value, then the exchange value is stored in the// destination. Otherwise, no opeation is performed.//// Arguments://// Destination (a0) - Supplies a pointer to the destination value.//// Exchange (a1) - Supplies the exchange.//// Comperand (a2) - Supplies the comperand value.//// Return Value://// The initial destination value is returned as the function value.////--
LEAF_ENTRY(InterlockedCompareExchange)
10: mb // synchronize memory accesss ldl_l v0, 0(a0) // get current addend value bis a1, zero, t0 // copy exchange value for store cmpeq v0, a2, t1 // check if operands match beq t1, 20f // if eq, operands mismatch stl_c t0, 0(a0) // store updated addend value beq t0,25f // if eq, store conditional failed mb // synchronize memory access20: ret zero, (ra) // return
//// We expect the store conditional will usually succeed the first time so it// is faster to branch forward (predicted not taken) to here and then branch// backward (predicted taken) to where we wanted to go.//
25: br zero, 10b // go try spin lock again
.end InterlockedCompareExchange SBTTL("Interlocked Exchange Add")//++//// LONG// InterlockedExchangeAdd (// IN PLONG Addend,// IN ULONG Increment// )//// Routine Description://// This function performs an interlocked add of an increment value to an// addend variable of type unsigned long. The initial value of the addend// variable is returned as the function value.//// Arguments://// Addend (a0) - Supplies a pointer to a variable whose value is to be// adjusted by the increment value.//// Increment (a1) - Supplies the increment value to be added to the// addend variable.//// Return Value://// The initial value of the addend variable.////--
LEAF_ENTRY(InterlockedExchangeAdd)
10: mb // synchronize memory access ldl_l v0, 0(a0) // get current addend value - locked addl v0, a1, t0 // increment addend value stl_c t0, 0(a0) // store updated value - conditionally beq t0, 20f // if eq, conditional store failed mb // synchronize memory access ret zero, (ra) // return
//// We expect the store conditional will usually succeed the first time so it// is faster to branch forward (predicted not taken) to here and then branch// backward (predicted taken) to where we wanted to go.//
20: br zero, 10b // go try spin lock again
.end InterlockedExchangeAdd
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