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Add a linear transform library to libutils

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Change-Id: Icdec5a6bebd9d8f24b3f335f8ec8b09a5810a774
This commit is contained in:
Jason Simmons 2011-06-28 17:43:30 -07:00
parent 2a5be6620b
commit c18d4da5e4
3 changed files with 327 additions and 0 deletions
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64
include/utils/LinearTransform.h Normal file
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@ -0,0 +1,64 @@
/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef _LIBS_UTILS_LINEAR_TRANSFORM_H
#define _LIBS_UTILS_LINEAR_TRANSFORM_H
#include <stdint.h>
namespace android {
// LinearTransform defines a structure which hold the definition of a
// transformation from single dimensional coordinate system A into coordinate
// system B (and back again). Values in A and in B are 64 bit, the linear
// scale factor is expressed as a rational number using two 32 bit values.
//
// Specifically, let
// f(a) = b
// F(b) = f^-1(b) = a
// then
//
// f(a) = (((a - a_zero) * a_to_b_numer) / a_to_b_denom) + b_zero;
//
// and
//
// F(b) = (((b - b_zero) * a_to_b_denom) / a_to_b_numer) + a_zero;
//
struct LinearTransform {
int64_t a_zero;
int64_t b_zero;
int32_t a_to_b_numer;
uint32_t a_to_b_denom;
// Transform from A->B
// Returns true on success, or false in the case of a singularity or an
// overflow.
bool doForwardTransform(int64_t a_in, int64_t* b_out) const;
// Transform from B->A
// Returns true on success, or false in the case of a singularity or an
// overflow.
bool doReverseTransform(int64_t b_in, int64_t* a_out) const;
// Helpers which will reduce the fraction N/D using Euclid's method.
template <class T> static void reduce(T* N, T* D);
static void reduce(int32_t* N, uint32_t* D);
};
}
#endif // _LIBS_UTILS_LINEAR_TRANSFORM_H

1
libs/utils/Android.mk
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@ -27,6 +27,7 @@ commonSources:= \
Debug.cpp \
FileMap.cpp \
Flattenable.cpp \
LinearTransform.cpp \
ObbFile.cpp \
Pool.cpp \
PropertyMap.cpp \

262
libs/utils/LinearTransform.cpp Normal file
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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#define __STDC_LIMIT_MACROS
#include <assert.h>
#include <stdint.h>
#include <utils/LinearTransform.h>
namespace android {
template<class T> static inline T ABS(T x) { return (x < 0) ? -x : x; }
// Static math methods involving linear transformations
static bool scale_u64_to_u64(
uint64_t val,
uint32_t N,
uint32_t D,
uint64_t* res,
bool round_up_not_down) {
uint64_t tmp1, tmp2;
uint32_t r;
assert(res);
assert(D);
// Let U32(X) denote a uint32_t containing the upper 32 bits of a 64 bit
// integer X.
// Let L32(X) denote a uint32_t containing the lower 32 bits of a 64 bit
// integer X.
// Let X[A, B] with A <= B denote bits A through B of the integer X.
// Let (A | B) denote the concatination of two 32 bit ints, A and B.
// IOW X = (A | B) => U32(X) == A && L32(X) == B
//
// compute M = val * N (a 96 bit int)
// ---------------------------------
// tmp2 = U32(val) * N (a 64 bit int)
// tmp1 = L32(val) * N (a 64 bit int)
// which means
// M = val * N = (tmp2 << 32) + tmp1
tmp2 = (val >> 32) * N;
tmp1 = (val & UINT32_MAX) * N;
// compute M[32, 95]
// tmp2 = tmp2 + U32(tmp1)
// = (U32(val) * N) + U32(L32(val) * N)
// = M[32, 95]
tmp2 += tmp1 >> 32;
// if M[64, 95] >= D, then M/D has bits > 63 set and we have
// an overflow.
if ((tmp2 >> 32) >= D) {
*res = UINT64_MAX;
return false;
}
// Divide. Going in we know
// tmp2 = M[32, 95]
// U32(tmp2) < D
r = tmp2 % D;
tmp2 /= D;
// At this point
// tmp1 = L32(val) * N
// tmp2 = M[32, 95] / D
// = (M / D)[32, 95]
// r = M[32, 95] % D
// U32(tmp2) = 0
//
// compute tmp1 = (r | M[0, 31])
tmp1 = (tmp1 & UINT32_MAX) | ((uint64_t)r << 32);
// Divide again. Keep the remainder around in order to round properly.
r = tmp1 % D;
tmp1 /= D;
// At this point
// tmp2 = (M / D)[32, 95]
// tmp1 = (M / D)[ 0, 31]
// r = M % D
// U32(tmp1) = 0
// U32(tmp2) = 0
// Pack the result and deal with the round-up case (As well as the
// remote possiblility over overflow in such a case).
*res = (tmp2 << 32) | tmp1;
if (r && round_up_not_down) {
++(*res);
if (!(*res)) {
*res = UINT64_MAX;
return false;
}
}
return true;
}
static bool linear_transform_s64_to_s64(
int64_t val,
int64_t basis1,
int32_t N,
uint32_t D,
int64_t basis2,
int64_t* out) {
uint64_t scaled, res;
uint64_t abs_val;
bool is_neg;
if (!out)
return false;
// Compute abs(val - basis_64). Keep track of whether or not this delta
// will be negative after the scale opertaion.
if (val < basis1) {
is_neg = true;
abs_val = basis1 - val;
} else {
is_neg = false;
abs_val = val - basis1;
}
if (N < 0)
is_neg = !is_neg;
if (!scale_u64_to_u64(abs_val,
ABS(N),
D,
&scaled,
is_neg))
return false; // overflow/undeflow
// if scaled is >= 0x8000<etc>, then we are going to overflow or
// underflow unless ABS(basis2) is large enough to pull us back into the
// non-overflow/underflow region.
if (scaled & INT64_MIN) {
if (is_neg && (basis2 < 0))
return false; // certain underflow
if (!is_neg && (basis2 >= 0))
return false; // certain overflow
if (ABS(basis2) <= static_cast<int64_t>(scaled & INT64_MAX))
return false; // not enough
// Looks like we are OK
*out = (is_neg ? (-scaled) : scaled) + basis2;
} else {
// Scaled fits within signed bounds, so we just need to check for
// over/underflow for two signed integers. Basically, if both scaled
// and basis2 have the same sign bit, and the result has a different
// sign bit, then we have under/overflow. An easy way to compute this
// is
// (scaled_signbit XNOR basis_signbit) &&
// (scaled_signbit XOR res_signbit)
// ==
// (scaled_signbit XOR basis_signbit XOR 1) &&
// (scaled_signbit XOR res_signbit)
if (is_neg)
scaled = -scaled;
res = scaled + basis2;
if ((scaled ^ basis2 ^ INT64_MIN) & (scaled ^ res) & INT64_MIN)
return false;
*out = res;
}
return true;
}
bool LinearTransform::doForwardTransform(int64_t a_in, int64_t* b_out) const {
if (0 == a_to_b_denom)
return false;
return linear_transform_s64_to_s64(a_in,
a_zero,
a_to_b_numer,
a_to_b_denom,
b_zero,
b_out);
}
bool LinearTransform::doReverseTransform(int64_t b_in, int64_t* a_out) const {
if (0 == a_to_b_numer)
return false;
return linear_transform_s64_to_s64(b_in,
b_zero,
a_to_b_denom,
a_to_b_numer,
a_zero,
a_out);
}
template <class T> void LinearTransform::reduce(T* N, T* D) {
T a, b;
if (!N || !D || !(*D)) {
assert(false);
return;
}
a = *N;
b = *D;
if (a == 0) {
*D = 1;
return;
}
// This implements Euclid's method to find GCD.
if (a < b) {
T tmp = a;
a = b;
b = tmp;
}
while (1) {
// a is now the greater of the two.
const T remainder = a % b;
if (remainder == 0) {
*N /= b;
*D /= b;
return;
}
// by swapping remainder and b, we are guaranteeing that a is
// still the greater of the two upon entrance to the loop.
a = b;
b = remainder;
}
};
template void LinearTransform::reduce<uint64_t>(uint64_t* N, uint64_t* D);
template void LinearTransform::reduce<uint32_t>(uint32_t* N, uint32_t* D);
void LinearTransform::reduce(int32_t* N, uint32_t* D) {
if (N && D && *D) {
if (*N < 0) {
*N = -(*N);
reduce(reinterpret_cast<uint32_t*>(N), D);
*N = -(*N);
} else {
reduce(reinterpret_cast<uint32_t*>(N), D);
}
}
}
} // namespace android