96 lines
3.2 KiB
Rust
96 lines
3.2 KiB
Rust
// Translated from C to Rust. The original C code can be found at
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// https://github.com/ulfjack/ryu and carries the following license:
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//
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// Copyright 2018 Ulf Adams
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//
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// The contents of this file may be used under the terms of the Apache License,
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// Version 2.0.
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//
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// (See accompanying file LICENSE-Apache or copy at
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// http://www.apache.org/licenses/LICENSE-2.0)
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//
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// Alternatively, the contents of this file may be used under the terms of
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// the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE-Boost or copy at
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// https://www.boost.org/LICENSE_1_0.txt)
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//
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// Unless required by applicable law or agreed to in writing, this software
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// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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// KIND, either express or implied.
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// Returns the number of decimal digits in v, which must not contain more than 9
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// digits.
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#[cfg_attr(feature = "no-panic", inline)]
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pub fn decimal_length9(v: u32) -> u32 {
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// Function precondition: v is not a 10-digit number.
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// (f2s: 9 digits are sufficient for round-tripping.)
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debug_assert!(v < 1000000000);
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if v >= 100000000 {
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9
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} else if v >= 10000000 {
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8
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} else if v >= 1000000 {
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7
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} else if v >= 100000 {
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6
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} else if v >= 10000 {
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5
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} else if v >= 1000 {
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4
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} else if v >= 100 {
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3
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} else if v >= 10 {
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2
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} else {
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1
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}
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}
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// Returns e == 0 ? 1 : [log_2(5^e)]; requires 0 <= e <= 3528.
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#[cfg_attr(feature = "no-panic", inline)]
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#[allow(dead_code)]
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pub fn log2_pow5(e: i32) -> i32 /* or u32 -> u32 */ {
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// This approximation works up to the point that the multiplication
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// overflows at e = 3529. If the multiplication were done in 64 bits, it
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// would fail at 5^4004 which is just greater than 2^9297.
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debug_assert!(e >= 0);
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debug_assert!(e <= 3528);
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((e as u32 * 1217359) >> 19) as i32
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}
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// Returns e == 0 ? 1 : ceil(log_2(5^e)); requires 0 <= e <= 3528.
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#[cfg_attr(feature = "no-panic", inline)]
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pub fn pow5bits(e: i32) -> i32 /* or u32 -> u32 */ {
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// This approximation works up to the point that the multiplication
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// overflows at e = 3529. If the multiplication were done in 64 bits, it
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// would fail at 5^4004 which is just greater than 2^9297.
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debug_assert!(e >= 0);
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debug_assert!(e <= 3528);
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(((e as u32 * 1217359) >> 19) + 1) as i32
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}
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#[cfg_attr(feature = "no-panic", inline)]
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#[allow(dead_code)]
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pub fn ceil_log2_pow5(e: i32) -> i32 /* or u32 -> u32 */ {
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log2_pow5(e) + 1
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}
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// Returns floor(log_10(2^e)); requires 0 <= e <= 1650.
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#[cfg_attr(feature = "no-panic", inline)]
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pub fn log10_pow2(e: i32) -> u32 /* or u32 -> u32 */ {
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// The first value this approximation fails for is 2^1651 which is just greater than 10^297.
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debug_assert!(e >= 0);
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debug_assert!(e <= 1650);
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(e as u32 * 78913) >> 18
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}
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// Returns floor(log_10(5^e)); requires 0 <= e <= 2620.
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#[cfg_attr(feature = "no-panic", inline)]
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pub fn log10_pow5(e: i32) -> u32 /* or u32 -> u32 */ {
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// The first value this approximation fails for is 5^2621 which is just greater than 10^1832.
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debug_assert!(e >= 0);
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debug_assert!(e <= 2620);
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(e as u32 * 732923) >> 20
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}
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