90 lines
2.2 KiB
ArmAsm
90 lines
2.2 KiB
ArmAsm
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// TITLE("Floating Point Round")
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//++
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//
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// Copyright (c) 1992 Digital Equipment Corporation
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//
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// Module Name:
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//
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// frnd.s
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//
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// Abstract:
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//
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// This module implements the floating round to integer function.
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//
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// Author:
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//
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// Thomas Van Baak (tvb) 07-Sep-1992
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//
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// Environment:
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//
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// Any mode.
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//
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// Revision History:
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//
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//--
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#include "ksalpha.h"
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SBTTL("Floating Round to Integer")
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//++
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//
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// DOUBLE
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// _frnd (
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// IN DOUBLE x
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// )
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//
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// Routine Description:
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//
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// This function rounds the given finite floating point argument to
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// an integer using nearest rounding.
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//
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// Arguments:
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//
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// x (f16) - Supplies the floating point value to be rounded.
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//
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// Return Value:
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//
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// The integer rounded floating point value is returned in f0.
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//
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// Implementation Notes:
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//
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//--
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LEAF_ENTRY(_frnd)
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//
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// If the absolute value of the argument is greater than or equal to 2^52,
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// then the argument is already an integer and it can be returned as the
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// function value. Note that 2^52 - 1 is the largest integer representable
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// by T-format (double) floating point because the mantissa (without the
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// hidden bit) is 52 bits wide.
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//
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fbeq f16, 10f // return if argument is 0.0
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ldt f10, Two52 // get 2^52 magic constant
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fabs f16, f11 // get absolute value of argument
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cmptlt f10, f11, f12 // is 2^52 < arg?
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fbeq f12, 20f // if eq[false], then do rounding
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10: cpys f16, f16, f0 // argument is return value
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ret zero, (ra) // return
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20: cpys f16, f10, f10 // if argument < 0, use -2^52 instead
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addt f16, f10, f0 // add [+-]2^52 (nearest rounding)
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subt f0, f10, f0 // subtract [+-]2^52 (nearest rounding)
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ret zero, (ra) // return
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.end _frnd
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//
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// Define floating point constants.
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//
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// (avoid ldit with floating point literal due to bug in acc/as that
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// creates writable .rdata sections - tvb)
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//
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.align 3
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.rdata
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Two52:
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.double 4503599627370496.0 // 2^52
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