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getSizeForCompression worst cases

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https://github.com/upx/upx/issues/463
	modified:   Makefile
	modified:   mem.cpp
This commit is contained in:
John Reiser 2021-02-25 20:04:16 -08:00 committed by Markus F.X.J. Oberhumer
parent 1ab6e01de2
commit 1c29f921e0
2 changed files with 28 additions and 4 deletions
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4
src/Makefile
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@ -9,8 +9,8 @@ MAKEFLAGS += -r
export SHELL = /bin/sh export SHELL = /bin/sh
# build configuration options for this Makefile # build configuration options for this Makefile
BUILD_TYPE_DEBUG ?= 0 BUILD_TYPE_DEBUG ?= 1
BUILD_TYPE_SANITIZE ?= 0 BUILD_TYPE_SANITIZE ?= 1
BUILD_USE_DEPEND ?= 1 BUILD_USE_DEPEND ?= 1
ifndef srcdir ifndef srcdir

28
src/mem.cpp
View File

@ -110,10 +110,34 @@ void MemBuffer::dealloc()
} }
static unsigned width(unsigned x)
{
unsigned w = 0;
if ((~0u << 16) & x) { w += 16; x >>= 16; }
if ((~0u << 8) & x) { w += 8; x >>= 8; }
if ((~0u << 4) & x) { w += 4; x >>= 4; }
if ((~0u << 2) & x) { w += 2; x >>= 2; }
if ((~0u << 1) & x) { w += 1; x >>= 1; }
return 1+ w;
}
static unsigned umax(unsigned a, unsigned b)
{
return (a >= b) ? a : b;
}
unsigned MemBuffer::getSizeForCompression(unsigned uncompressed_size, unsigned extra) unsigned MemBuffer::getSizeForCompression(unsigned uncompressed_size, unsigned extra)
{ {
size_t bytes = mem_size(1, uncompressed_size, extra); size_t const z = uncompressed_size; // fewer keystrokes and display columns
bytes += uncompressed_size/8 + 256; size_t bytes = mem_size(1, z, extra);
size_t const w = umax(8, width(z -1)); // ignore tiny offsets
bytes = 256 + // safety?
umax(bytes + z/8, // All literal: 1 bit overhead per literal byte
// Worst matching: All match at max_offset, which implies 3==min_match
// NRV2B: 1 byte plus 2 bits per width exceeding 8 ("ss11")
umax((z/3 * (8+ 2*(w - 8)/1))/8,
// NRV2E: 1 byte plus 3 bits per pair of width exceeding 7 ("ss12")
(z/3 * (8+ 3*(w - 7)/2))/8 ) );
return ACC_ICONV(unsigned, bytes); return ACC_ICONV(unsigned, bytes);
} }