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Improve exp2's precision to 20-24 bits.

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The exp2 function was approximated using lolremez, achieving an
accuracy of less than 2*10^-7 within the range of 0 to 1.

Signed-off-by: Jean-Marc Valin <jeanmarcv@google.com>
This commit is contained in:
Yunho Huh 2024-11-02 13:02:16 -04:00 • committed by Jean-Marc Valin
parent 7fa23b4ed0
commit 255f013035
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GPG key ID: 8D2952BBB52C646D
2 changed files with 38 additions and 9 deletions
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20
celt/tests/test_unit_mathops.c
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@ -1,6 +1,7 @@
/* Copyright (c) 2008-2011 Xiph.Org Foundation, Mozilla Corporation,
Gregory Maxwell
Written by Jean-Marc Valin, Gregory Maxwell, and Timothy B. Terriberry */
Written by Jean-Marc Valin, Gregory Maxwell, Timothy B. Terriberry,
and Yunho Huh */
/*
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
@ -170,21 +171,32 @@ void testlog2(void)
void testexp2(void)
{
float x;
float error_threshold = 2.3e-07;
float max_error = 0;
for (x=-11.0;x<24.0;x+=0.0007f)
{
float error = fabs(x-(1.442695040888963387*log(celt_exp2(x))));
if (error>0.0002)
if (max_error < error)
{
fprintf (stderr, "celt_exp2 failed: fabs(x-(1.442695040888963387*log(celt_exp2(x))))>0.0005 (x = %f, error = %f)\n", x,error);
max_error = error;
}
if (error > error_threshold)
{
fprintf (stderr,
"celt_exp2 failed: "
"fabs(x-(1.442695040888963387*log(celt_exp2(x))))>%15.25e "
"(x = %f, error = %15.25e)\n", error_threshold, x, error);
ret = 1;
}
}
fprintf (stdout, "celt_exp2 max_error: %15.25e\n", max_error);
}
void testexp2log2(void)
{
float x;
float error_threshold = 5.0e-04;
float error_threshold = 2.0e-06;
float max_error = 0;
for (x=-11.0;x<24.0;x+=0.0007f)
{