// Copyright (c) 2011 The Chromium Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #include "butil/rand_util.h" #include <math.h> #include <algorithm> #include <limits> #include "butil/basictypes.h" #include "butil/logging.h" #include "butil/strings/string_util.h" namespace butil { int RandInt(int min, int max) { DCHECK_LE(min, max); uint64_t range = static_cast<uint64_t>(max) - min + 1; int result = min + static_cast<int>(butil::RandGenerator(range)); DCHECK_GE(result, min); DCHECK_LE(result, max); return result; } double RandDouble() { return BitsToOpenEndedUnitInterval(butil::RandUint64()); } double BitsToOpenEndedUnitInterval(uint64_t bits) { // We try to get maximum precision by masking out as many bits as will fit // in the target type's mantissa, and raising it to an appropriate power to // produce output in the range [0, 1). For IEEE 754 doubles, the mantissa // is expected to accommodate 53 bits. COMPILE_ASSERT(std::numeric_limits<double>::radix == 2, otherwise_use_scalbn); static const int kBits = std::numeric_limits<double>::digits; uint64_t random_bits = bits & ((GG_UINT64_C(1) << kBits) - 1); double result = ldexp(static_cast<double>(random_bits), -1 * kBits); DCHECK_GE(result, 0.0); DCHECK_LT(result, 1.0); return result; } uint64_t RandGenerator(uint64_t range) { DCHECK_GT(range, 0u); // We must discard random results above this number, as they would // make the random generator non-uniform (consider e.g. if // MAX_UINT64 was 7 and |range| was 5, then a result of 1 would be twice // as likely as a result of 3 or 4). uint64_t max_acceptable_value = (std::numeric_limits<uint64_t>::max() / range) * range - 1; uint64_t value; do { value = butil::RandUint64(); } while (value > max_acceptable_value); return value % range; } std::string RandBytesAsString(size_t length) { DCHECK_GT(length, 0u); std::string result; RandBytes(WriteInto(&result, length + 1), length); return result; } } // namespace butil