зеркало из https://github.com/mozilla/pjs.git
199 строки
6.2 KiB
C++
199 строки
6.2 KiB
C++
/* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is Mozilla code.
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*
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* The Initial Developer of the Original Code is
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* the Mozilla Foundation.
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* Portions created by the Initial Developer are Copyright (C) 2010
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Chris Pearce <chris@pearce.org.nz>
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either the GNU General Public License Version 2 or later (the "GPL"), or
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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#include "VideoUtils.h"
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#include "prtypes.h"
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// Adds two 32bit unsigned numbers, retuns PR_TRUE if addition succeeded,
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// or PR_FALSE the if addition would result in an overflow.
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PRBool AddOverflow32(PRUint32 a, PRUint32 b, PRUint32& aResult) {
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PRUint64 rl = static_cast<PRUint64>(a) + static_cast<PRUint64>(b);
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if (rl > PR_UINT32_MAX) {
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return PR_FALSE;
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}
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aResult = static_cast<PRUint32>(rl);
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return true;
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}
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PRBool MulOverflow32(PRUint32 a, PRUint32 b, PRUint32& aResult)
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{
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// 32 bit integer multiplication with overflow checking. Returns PR_TRUE
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// if the multiplication was successful, or PR_FALSE if the operation resulted
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// in an integer overflow.
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PRUint64 a64 = a;
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PRUint64 b64 = b;
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PRUint64 r64 = a64 * b64;
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if (r64 > PR_UINT32_MAX)
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return PR_FALSE;
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aResult = static_cast<PRUint32>(r64);
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return PR_TRUE;
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}
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// Adds two 64bit numbers, retuns PR_TRUE if addition succeeded, or PR_FALSE
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// if addition would result in an overflow.
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PRBool AddOverflow(PRInt64 a, PRInt64 b, PRInt64& aResult) {
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if (b < 1) {
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if (PR_INT64_MIN - b <= a) {
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aResult = a + b;
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return PR_TRUE;
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}
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} else if (PR_INT64_MAX - b >= a) {
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aResult = a + b;
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return PR_TRUE;
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}
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return PR_FALSE;
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}
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// 64 bit integer multiplication with overflow checking. Returns PR_TRUE
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// if the multiplication was successful, or PR_FALSE if the operation resulted
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// in an integer overflow.
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PRBool MulOverflow(PRInt64 a, PRInt64 b, PRInt64& aResult) {
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// We break a multiplication a * b into of sign_a * sign_b * abs(a) * abs(b)
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//
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// This is equivalent to:
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//
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// (sign_a * sign_b) * ((a_hi * 2^32) + a_lo) * ((b_hi * 2^32) + b_lo)
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//
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// Which is equivalent to:
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//
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// (sign_a * sign_b) *
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// ((a_hi * b_hi << 64) +
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// (a_hi * b_lo << 32) + (a_lo * b_hi << 32) +
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// a_lo * b_lo)
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//
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// So to check if a*b overflows, we must check each sub part of the above
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// sum.
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//
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// Note: -1 * PR_INT64_MIN == PR_INT64_MIN ; we can't negate PR_INT64_MIN!
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// Note: Shift of negative numbers is undefined.
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//
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// Figure out the sign after multiplication. Then we can just work with
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// unsigned numbers.
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PRInt64 sign = (!(a < 0) == !(b < 0)) ? 1 : -1;
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PRInt64 abs_a = (a < 0) ? -a : a;
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PRInt64 abs_b = (b < 0) ? -b : b;
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if (abs_a < 0) {
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NS_ASSERTION(a == PR_INT64_MIN, "How else can this happen?");
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if (b == 0 || b == 1) {
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aResult = a * b;
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return PR_TRUE;
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} else {
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return PR_FALSE;
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}
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}
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if (abs_b < 0) {
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NS_ASSERTION(b == PR_INT64_MIN, "How else can this happen?");
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if (a == 0 || a == 1) {
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aResult = a * b;
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return PR_TRUE;
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} else {
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return PR_FALSE;
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}
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}
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NS_ASSERTION(abs_a >= 0 && abs_b >= 0, "abs values must be non-negative");
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PRInt64 a_hi = abs_a >> 32;
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PRInt64 a_lo = abs_a & 0xFFFFFFFF;
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PRInt64 b_hi = abs_b >> 32;
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PRInt64 b_lo = abs_b & 0xFFFFFFFF;
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NS_ASSERTION((a_hi<<32) + a_lo == abs_a, "Partition must be correct");
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NS_ASSERTION((b_hi<<32) + b_lo == abs_b, "Partition must be correct");
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// In the sub-equation (a_hi * b_hi << 64), if a_hi or b_hi
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// are non-zero, this will overflow as it's shifted by 64.
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// Abort if this overflows.
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if (a_hi != 0 && b_hi != 0) {
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return PR_FALSE;
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}
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// We can now assume that either a_hi or b_hi is 0.
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NS_ASSERTION(a_hi == 0 || b_hi == 0, "One of these must be 0");
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// Next we calculate:
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// (a_hi * b_lo << 32) + (a_lo * b_hi << 32)
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// We can factor this as:
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// (a_hi * b_lo + a_lo * b_hi) << 32
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PRInt64 q = a_hi * b_lo + a_lo * b_hi;
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if (q > PR_INT32_MAX) {
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// q will overflow when we shift by 32; abort.
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return PR_FALSE;
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}
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q <<= 32;
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// Both a_lo and b_lo are less than INT32_MAX, so can't overflow.
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PRUint64 lo = a_lo * b_lo;
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if (lo > PR_INT64_MAX) {
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return PR_FALSE;
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}
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// Add the final result. We must check for overflow during addition.
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if (!AddOverflow(q, static_cast<PRInt64>(lo), aResult)) {
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return PR_FALSE;
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}
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aResult *= sign;
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NS_ASSERTION(a * b == aResult, "We didn't overflow, but result is wrong!");
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return PR_TRUE;
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}
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// Converts from number of audio samples to milliseconds, given the specified
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// audio rate.
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PRBool SamplesToMs(PRInt64 aSamples, PRUint32 aRate, PRInt64& aOutMs)
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{
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PRInt64 x;
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if (!MulOverflow(aSamples, 1000, x))
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return PR_FALSE;
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aOutMs = x / aRate;
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return PR_TRUE;
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}
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// Converts from milliseconds to number of audio samples, given the specified
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// audio rate.
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PRBool MsToSamples(PRInt64 aMs, PRUint32 aRate, PRInt64& aOutSamples)
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{
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PRInt64 x;
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if (!MulOverflow(aMs, aRate, x))
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return PR_FALSE;
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aOutSamples = x / 1000;
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return PR_TRUE;
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}
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