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//===- FakeQuantSupport.cpp - Support utilities for FakeQuant ops ---------===//
//
// Copyright 2019 The MLIR Authors.
//
// 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.
// =============================================================================
#include "mlir/Quantization/FakeQuantSupport.h"
#include "mlir/Quantization/QuantTypes.h"
using namespace mlir;
using namespace mlir::quant;
UniformQuantizedType mlir::quant::fakeQuantAttrsToType(Location loc,
unsigned numBits,
double rmin, double rmax,
bool narrowRange,
Type expressedType) {
MLIRContext *ctx = expressedType.getContext();
Type storageType;
unsigned flags;
int64_t qmin;
int64_t qmax;
// Hard-coded type mapping from TFLite.
if (numBits <= 8) {
storageType = IntegerType::get(8, ctx);
flags = 0;
qmin = 0;
qmax = 255;
} else if (numBits <= 16) {
storageType = IntegerType::get(16, ctx);
flags = QuantizationFlags::Signed;
qmin = -32768;
qmax = 32767;
} else {
ctx->emitError(loc, "unsupported FakeQuant number of bits: ") << numBits;
return nullptr;
}
// Handle narrowRange.
if (narrowRange) {
qmin += 1;
}
// Range must straddle zero.
if (rmin > 0.0 || rmax < 0.0) {
return (ctx->emitError(loc, "FakeQuant range must straddle zero: [")
<< rmin << "," << rmax << "]",
nullptr);
}
// Special case where min/max is a point. Must be 0.
if (rmin == rmax) {
return UniformQuantizedType::getChecked(flags, storageType, expressedType,
0.0, 0, qmin, qmax, loc);
}
// Determine the scale.
const double qminDouble = qmin;
const double qmaxDouble = qmax;
const double scale = (rmax - rmin) / (qmaxDouble - qminDouble);
// Zero point computation.
// In float, solve the affine equation for any known pair
// (real value, corresponding quantized value), of which, two such pairs
// are known: (rmin, qmin), (rmax, qmax).
// The arithmetic error on the zero point computed from either pair will be
// roughly machine_epsilon * (sum of absolute values of terms).
// Use the variant that adds the smaller error.
const double zeroPointFromMin = qminDouble - rmin / scale;
const double zeroPointFromMinError =
std::abs(qminDouble) + std::abs(rmin / scale);
const double zeroPointFromMax = qmaxDouble - rmax / scale;
const double zeroPointFromMaxError =
std::abs(qmaxDouble) + std::abs(rmax / scale);
const double zeroPointDouble = (zeroPointFromMinError < zeroPointFromMaxError)
? zeroPointFromMin
: zeroPointFromMax;
// Now nudge the zero point to be an integer.
int64_t nudgedZeroPoint = 0;
if (zeroPointDouble < qminDouble) {
nudgedZeroPoint = qmin;
} else if (zeroPointDouble > qmaxDouble) {
nudgedZeroPoint = qmax;
} else {
nudgedZeroPoint = round(zeroPointDouble);
}
// By construction, the nudged zero point should always be in range.
assert(nudgedZeroPoint >= qmin);
assert(nudgedZeroPoint <= qmax);
return UniformQuantizedType::getChecked(flags, storageType, expressedType,
scale, nudgedZeroPoint, qmin, qmax,
loc);
}
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