From 119e9db233ad0f4cbd4cfb9f9385a7bca378b37d Mon Sep 17 00:00:00 2001 From: Zeng Chi Date: Mon, 21 Sep 2026 18:24:42 +0800 Subject: KVM: Don't pre-reserve xarray entries when storing empty/NULL attributes Skip the xarray reservation loop when clearing all memory attributes, as storing NULL only erases the entry and never needs to allocate, so no reservation (and no cleanup of a failed one) is required in that case. Suggested-by: Sean Christopherson Cc: David Ballesteros Signed-off-by: Zeng Chi Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com [sean: split to separate patch] Signed-off-by: Sean Christopherson --- lib/math/int_log.c | 133 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 133 insertions(+) create mode 100644 lib/math/int_log.c (limited to 'lib/math/int_log.c') diff --git a/lib/math/int_log.c b/lib/math/int_log.c new file mode 100644 index 000000000..8f9da3a2a --- /dev/null +++ b/lib/math/int_log.c @@ -0,0 +1,133 @@ +// SPDX-License-Identifier: LGPL-2.1-or-later +/* + * Provides fixed-point logarithm operations. + * + * Copyright (C) 2006 Christoph Pfister (christophpfister@gmail.com) + */ + +#include +#include +#include +#include +#include + +#include + +static const unsigned short logtable[256] = { + 0x0000, 0x0171, 0x02e0, 0x044e, 0x05ba, 0x0725, 0x088e, 0x09f7, + 0x0b5d, 0x0cc3, 0x0e27, 0x0f8a, 0x10eb, 0x124b, 0x13aa, 0x1508, + 0x1664, 0x17bf, 0x1919, 0x1a71, 0x1bc8, 0x1d1e, 0x1e73, 0x1fc6, + 0x2119, 0x226a, 0x23ba, 0x2508, 0x2656, 0x27a2, 0x28ed, 0x2a37, + 0x2b80, 0x2cc8, 0x2e0f, 0x2f54, 0x3098, 0x31dc, 0x331e, 0x345f, + 0x359f, 0x36de, 0x381b, 0x3958, 0x3a94, 0x3bce, 0x3d08, 0x3e41, + 0x3f78, 0x40af, 0x41e4, 0x4319, 0x444c, 0x457f, 0x46b0, 0x47e1, + 0x4910, 0x4a3f, 0x4b6c, 0x4c99, 0x4dc5, 0x4eef, 0x5019, 0x5142, + 0x526a, 0x5391, 0x54b7, 0x55dc, 0x5700, 0x5824, 0x5946, 0x5a68, + 0x5b89, 0x5ca8, 0x5dc7, 0x5ee5, 0x6003, 0x611f, 0x623a, 0x6355, + 0x646f, 0x6588, 0x66a0, 0x67b7, 0x68ce, 0x69e4, 0x6af8, 0x6c0c, + 0x6d20, 0x6e32, 0x6f44, 0x7055, 0x7165, 0x7274, 0x7383, 0x7490, + 0x759d, 0x76aa, 0x77b5, 0x78c0, 0x79ca, 0x7ad3, 0x7bdb, 0x7ce3, + 0x7dea, 0x7ef0, 0x7ff6, 0x80fb, 0x81ff, 0x8302, 0x8405, 0x8507, + 0x8608, 0x8709, 0x8809, 0x8908, 0x8a06, 0x8b04, 0x8c01, 0x8cfe, + 0x8dfa, 0x8ef5, 0x8fef, 0x90e9, 0x91e2, 0x92db, 0x93d2, 0x94ca, + 0x95c0, 0x96b6, 0x97ab, 0x98a0, 0x9994, 0x9a87, 0x9b7a, 0x9c6c, + 0x9d5e, 0x9e4f, 0x9f3f, 0xa02e, 0xa11e, 0xa20c, 0xa2fa, 0xa3e7, + 0xa4d4, 0xa5c0, 0xa6ab, 0xa796, 0xa881, 0xa96a, 0xaa53, 0xab3c, + 0xac24, 0xad0c, 0xadf2, 0xaed9, 0xafbe, 0xb0a4, 0xb188, 0xb26c, + 0xb350, 0xb433, 0xb515, 0xb5f7, 0xb6d9, 0xb7ba, 0xb89a, 0xb97a, + 0xba59, 0xbb38, 0xbc16, 0xbcf4, 0xbdd1, 0xbead, 0xbf8a, 0xc065, + 0xc140, 0xc21b, 0xc2f5, 0xc3cf, 0xc4a8, 0xc580, 0xc658, 0xc730, + 0xc807, 0xc8de, 0xc9b4, 0xca8a, 0xcb5f, 0xcc34, 0xcd08, 0xcddc, + 0xceaf, 0xcf82, 0xd054, 0xd126, 0xd1f7, 0xd2c8, 0xd399, 0xd469, + 0xd538, 0xd607, 0xd6d6, 0xd7a4, 0xd872, 0xd93f, 0xda0c, 0xdad9, + 0xdba5, 0xdc70, 0xdd3b, 0xde06, 0xded0, 0xdf9a, 0xe063, 0xe12c, + 0xe1f5, 0xe2bd, 0xe385, 0xe44c, 0xe513, 0xe5d9, 0xe69f, 0xe765, + 0xe82a, 0xe8ef, 0xe9b3, 0xea77, 0xeb3b, 0xebfe, 0xecc1, 0xed83, + 0xee45, 0xef06, 0xefc8, 0xf088, 0xf149, 0xf209, 0xf2c8, 0xf387, + 0xf446, 0xf505, 0xf5c3, 0xf680, 0xf73e, 0xf7fb, 0xf8b7, 0xf973, + 0xfa2f, 0xfaea, 0xfba5, 0xfc60, 0xfd1a, 0xfdd4, 0xfe8e, 0xff47, +}; + +unsigned int intlog2(u32 value) +{ + /** + * returns: log2(value) * 2^24 + * wrong result if value = 0 (log2(0) is undefined) + */ + unsigned int msb; + unsigned int logentry; + unsigned int significand; + unsigned int interpolation; + + if (unlikely(value == 0)) { + WARN_ON(1); + return 0; + } + + /* first detect the msb (count begins at 0) */ + msb = fls(value) - 1; + + /** + * now we use a logtable after the following method: + * + * log2(2^x * y) * 2^24 = x * 2^24 + log2(y) * 2^24 + * where x = msb and therefore 1 <= y < 2 + * first y is determined by shifting the value left + * so that msb is bit 31 + * 0x00231f56 -> 0x8C7D5800 + * the result is y * 2^31 -> "significand" + * then the highest 9 bits are used for a table lookup + * the highest bit is discarded because it's always set + * the highest nine bits in our example are 100011000 + * so we would use the entry 0x18 + */ + significand = value << (31 - msb); + logentry = (significand >> 23) % ARRAY_SIZE(logtable); + + /** + * last step we do is interpolation because of the + * limitations of the log table the error is that part of + * the significand which isn't used for lookup then we + * compute the ratio between the error and the next table entry + * and interpolate it between the log table entry used and the + * next one the biggest error possible is 0x7fffff + * (in our example it's 0x7D5800) + * needed value for next table entry is 0x800000 + * so the interpolation is + * (error / 0x800000) * (logtable_next - logtable_current) + * in the implementation the division is moved to the end for + * better accuracy there is also an overflow correction if + * logtable_next is 256 + */ + interpolation = ((significand & 0x7fffff) * + ((logtable[(logentry + 1) % ARRAY_SIZE(logtable)] - + logtable[logentry]) & 0xffff)) >> 15; + + /* now we return the result */ + return ((msb << 24) + (logtable[logentry] << 8) + interpolation); +} +EXPORT_SYMBOL(intlog2); + +unsigned int intlog10(u32 value) +{ + /** + * returns: log10(value) * 2^24 + * wrong result if value = 0 (log10(0) is undefined) + */ + u64 log; + + if (unlikely(value == 0)) { + WARN_ON(1); + return 0; + } + + log = intlog2(value); + + /** + * we use the following method: + * log10(x) = log2(x) * log10(2) + */ + + return (log * 646456993) >> 31; +} +EXPORT_SYMBOL(intlog10); -- cgit v1.3.1