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COPYING.txt

author | Ryan C. Gordon <icculus@icculus.org> |

Tue, 15 May 2018 01:04:11 -0400 | |

changeset 11987 | 0c284754e25b |

parent 11811 | 5d94cb6b24d3 |

child 12503 | 806492103856 |

permissions | -rw-r--r-- |

audio: converting int32 to/from float shouldn't use doubles.

The concern is that a massive int sample, like 0x7FFFFFFF, won't fit in a

float32, which doesn't have enough bits to hold a whole number this large,

just to divide it to get a value between 0 and 1.

Previously we would convert to double, to get more bits, do the division, and

cast back to a float, but this is expensive.

Casting to double is more accurate, but it's 2x to 3x slower. Shifting out

the least significant byte of an int32, so it'll definitely fit in a float,

and dividing by 0x7FFFFF is still accurate to about 5 decimal places, and the

difference doesn't appear to be perceptable.

The concern is that a massive int sample, like 0x7FFFFFFF, won't fit in a

float32, which doesn't have enough bits to hold a whole number this large,

just to divide it to get a value between 0 and 1.

Previously we would convert to double, to get more bits, do the division, and

cast back to a float, but this is expensive.

Casting to double is more accurate, but it's 2x to 3x slower. Shifting out

the least significant byte of an int32, so it'll definitely fit in a float,

and dividing by 0x7FFFFF is still accurate to about 5 decimal places, and the

difference doesn't appear to be perceptable.

2 Simple DirectMedia Layer

3 Copyright (C) 1997-2018 Sam Lantinga <slouken@libsdl.org>

5 This software is provided 'as-is', without any express or implied

6 warranty. In no event will the authors be held liable for any damages

7 arising from the use of this software.

9 Permission is granted to anyone to use this software for any purpose,

10 including commercial applications, and to alter it and redistribute it

11 freely, subject to the following restrictions:

13 1. The origin of this software must not be misrepresented; you must not

14 claim that you wrote the original software. If you use this software

15 in a product, an acknowledgment in the product documentation would be

16 appreciated but is not required.

17 2. Altered source versions must be plainly marked as such, and must not be

18 misrepresented as being the original software.

19 3. This notice may not be removed or altered from any source distribution.