gecko/content/media/VideoUtils.cpp

199 lines
6.3 KiB
C++

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