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zig/lib/std/fmt/parse_float.zig

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// Adapted from https://github.com/grzegorz-kraszewski/stringtofloat.
// MIT License
//
// Copyright (c) 2016 Grzegorz Kraszewski
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
// Be aware that this implementation has the following limitations:
//
// - Is not round-trip accurate for all values
// - Only supports round-to-zero
// - Does not handle denormals
const std = @import("../std.zig");
const ascii = std.ascii;
const max_digits = 25;
const f64_plus_zero: u64 = 0x0000000000000000;
const f64_minus_zero: u64 = 0x8000000000000000;
const f64_plus_infinity: u64 = 0x7FF0000000000000;
const f64_minus_infinity: u64 = 0xFFF0000000000000;
const Z96 = struct {
d0: u32,
d1: u32,
d2: u32,
// d = s >> 1
inline fn shiftRight1(d: *Z96, s: Z96) void {
d.d0 = (s.d0 >> 1) | ((s.d1 & 1) << 31);
d.d1 = (s.d1 >> 1) | ((s.d2 & 1) << 31);
d.d2 = s.d2 >> 1;
}
// d = s << 1
inline fn shiftLeft1(d: *Z96, s: Z96) void {
d.d2 = (s.d2 << 1) | ((s.d1 & (1 << 31)) >> 31);
d.d1 = (s.d1 << 1) | ((s.d0 & (1 << 31)) >> 31);
d.d0 = s.d0 << 1;
}
// d += s
inline fn add(d: *Z96, s: Z96) void {
var w = @as(u64, d.d0) + @as(u64, s.d0);
d.d0 = @truncate(u32, w);
w >>= 32;
w += @as(u64, d.d1) + @as(u64, s.d1);
d.d1 = @truncate(u32, w);
w >>= 32;
w += @as(u64, d.d2) + @as(u64, s.d2);
d.d2 = @truncate(u32, w);
}
// d -= s
inline fn sub(d: *Z96, s: Z96) void {
var w = @as(u64, d.d0) -% @as(u64, s.d0);
d.d0 = @truncate(u32, w);
w >>= 32;
w += @as(u64, d.d1) -% @as(u64, s.d1);
d.d1 = @truncate(u32, w);
w >>= 32;
w += @as(u64, d.d2) -% @as(u64, s.d2);
d.d2 = @truncate(u32, w);
}
};
const FloatRepr = struct {
negative: bool,
exponent: i32,
mantissa: u64,
};
fn convertRepr(comptime T: type, n: FloatRepr) T {
const mask28: u32 = 0xf << 28;
var s: Z96 = undefined;
var q: Z96 = undefined;
var r: Z96 = undefined;
s.d0 = @truncate(u32, n.mantissa);
s.d1 = @truncate(u32, n.mantissa >> 32);
s.d2 = 0;
var binary_exponent: i32 = 92;
var exp = n.exponent;
while (exp > 0) : (exp -= 1) {
q.shiftLeft1(s); // q = p << 1
r.shiftLeft1(q); // r = p << 2
s.shiftLeft1(r); // p = p << 3
s.add(q); // p = (p << 3) + (p << 1)
while (s.d2 & mask28 != 0) {
q.shiftRight1(s);
binary_exponent += 1;
s = q;
}
}
while (exp < 0) {
while (s.d2 & (1 << 31) == 0) {
q.shiftLeft1(s);
binary_exponent -= 1;
s = q;
}
q.d2 = s.d2 / 10;
r.d1 = s.d2 % 10;
r.d2 = (s.d1 >> 8) | (r.d1 << 24);
q.d1 = r.d2 / 10;
r.d1 = r.d2 % 10;
r.d2 = ((s.d1 & 0xff) << 16) | (s.d0 >> 16) | (r.d1 << 24);
r.d0 = r.d2 / 10;
r.d1 = r.d2 % 10;
q.d1 = (q.d1 << 8) | ((r.d0 & 0x00ff0000) >> 16);
q.d0 = r.d0 << 16;
r.d2 = (s.d0 *% 0xffff) | (r.d1 << 16);
q.d0 |= r.d2 / 10;
s = q;
exp += 1;
}
if (s.d0 != 0 or s.d1 != 0 or s.d2 != 0) {
while (s.d2 & mask28 == 0) {
q.shiftLeft1(s);
binary_exponent -= 1;
s = q;
}
}
binary_exponent += 1023;
const repr: u64 = blk: {
if (binary_exponent > 2046) {
break :blk if (n.negative) f64_minus_infinity else f64_plus_infinity;
} else if (binary_exponent < 1) {
break :blk if (n.negative) f64_minus_zero else f64_plus_zero;
} else if (s.d2 != 0) {
const binexs2 = @intCast(u64, binary_exponent) << 52;
const rr = (@as(u64, s.d2 & ~mask28) << 24) | ((@as(u64, s.d1) + 128) >> 8) | binexs2;
break :blk if (n.negative) rr | (1 << 63) else rr;
} else {
break :blk 0;
}
};
const f = @bitCast(f64, repr);
return @floatCast(T, f);
}
const State = enum {
MaybeSign,
LeadingMantissaZeros,
LeadingFractionalZeros,
MantissaIntegral,
MantissaFractional,
ExponentSign,
LeadingExponentZeros,
Exponent,
};
const ParseResult = enum {
Ok,
PlusZero,
MinusZero,
PlusInf,
MinusInf,
};
fn parseRepr(s: []const u8, n: *FloatRepr) !ParseResult {
var digit_index: usize = 0;
var negative = false;
var negative_exp = false;
var exponent: i32 = 0;
var state = State.MaybeSign;
var i: usize = 0;
while (i < s.len) {
const c = s[i];
switch (state) {
.MaybeSign => {
state = .LeadingMantissaZeros;
if (c == '+') {
i += 1;
} else if (c == '-') {
n.negative = true;
i += 1;
} else if (ascii.isDigit(c) or c == '.') {
// continue
} else {
return error.InvalidCharacter;
}
},
.LeadingMantissaZeros => {
if (c == '0') {
i += 1;
} else if (c == '.') {
i += 1;
state = .LeadingFractionalZeros;
} else {
state = .MantissaIntegral;
}
},
.LeadingFractionalZeros => {
if (c == '0') {
i += 1;
if (n.exponent > std.math.minInt(i32)) {
n.exponent -= 1;
}
} else {
state = .MantissaFractional;
}
},
.MantissaIntegral => {
if (ascii.isDigit(c)) {
if (digit_index < max_digits) {
n.mantissa *%= 10;
n.mantissa += c - '0';
digit_index += 1;
} else if (n.exponent < std.math.maxInt(i32)) {
n.exponent += 1;
}
i += 1;
} else if (c == '.') {
i += 1;
state = .MantissaFractional;
} else {
state = .MantissaFractional;
}
},
.MantissaFractional => {
if (ascii.isDigit(c)) {
if (digit_index < max_digits) {
n.mantissa *%= 10;
n.mantissa += c - '0';
n.exponent -%= 1;
digit_index += 1;
}
i += 1;
} else if (c == 'e' or c == 'E') {
i += 1;
state = .ExponentSign;
} else {
state = .ExponentSign;
}
},
.ExponentSign => {
if (c == '+') {
i += 1;
} else if (c == '-') {
negative_exp = true;
i += 1;
}
state = .LeadingExponentZeros;
},
.LeadingExponentZeros => {
if (c == '0') {
i += 1;
} else {
state = .Exponent;
}
},
.Exponent => {
if (ascii.isDigit(c)) {
if (exponent < std.math.maxInt(i32) / 10) {
exponent *= 10;
exponent += @intCast(i32, c - '0');
}
i += 1;
} else {
return error.InvalidCharacter;
}
},
}
}
if (negative_exp) exponent = -exponent;
n.exponent += exponent;
if (n.mantissa == 0) {
return if (n.negative) .MinusZero else .PlusZero;
} else if (n.exponent > 309) {
return if (n.negative) .MinusInf else .PlusInf;
} else if (n.exponent < -328) {
return if (n.negative) .MinusZero else .PlusZero;
}
return .Ok;
}
fn caseInEql(a: []const u8, b: []const u8) bool {
if (a.len != b.len) return false;
for (a) |_, i| {
if (ascii.toUpper(a[i]) != ascii.toUpper(b[i])) {
return false;
}
}
return true;
}
pub fn parseFloat(comptime T: type, s: []const u8) !T {
if (s.len == 0) {
return error.InvalidCharacter;
}
if (caseInEql(s, "nan")) {
return std.math.nan(T);
} else if (caseInEql(s, "inf") or caseInEql(s, "+inf")) {
return std.math.inf(T);
} else if (caseInEql(s, "-inf")) {
return -std.math.inf(T);
}
var r = FloatRepr{
.negative = false,
.exponent = 0,
.mantissa = 0,
};
return switch (try parseRepr(s, &r)) {
.Ok => convertRepr(T, r),
.PlusZero => 0.0,
.MinusZero => -@as(T, 0.0),
.PlusInf => std.math.inf(T),
.MinusInf => -std.math.inf(T),
};
}
test "fmt.parseFloat" {
const testing = std.testing;
const expect = testing.expect;
const expectEqual = testing.expectEqual;
const approxEq = std.math.approxEq;
const epsilon = 1e-7;
inline for ([_]type{ f16, f32, f64, f128 }) |T| {
const Z = std.meta.Int(false, T.bit_count);
testing.expectError(error.InvalidCharacter, parseFloat(T, ""));
testing.expectError(error.InvalidCharacter, parseFloat(T, " 1"));
testing.expectError(error.InvalidCharacter, parseFloat(T, "1abc"));
expectEqual(try parseFloat(T, "0"), 0.0);
expectEqual(try parseFloat(T, "0"), 0.0);
expectEqual(try parseFloat(T, "+0"), 0.0);
expectEqual(try parseFloat(T, "-0"), 0.0);
expectEqual(try parseFloat(T, "0e0"), 0);
expectEqual(try parseFloat(T, "2e3"), 2000.0);
expectEqual(try parseFloat(T, "1e0"), 1.0);
expectEqual(try parseFloat(T, "-2e3"), -2000.0);
expectEqual(try parseFloat(T, "-1e0"), -1.0);
expectEqual(try parseFloat(T, "1.234e3"), 1234);
expect(approxEq(T, try parseFloat(T, "3.141"), 3.141, epsilon));
expect(approxEq(T, try parseFloat(T, "-3.141"), -3.141, epsilon));
expectEqual(try parseFloat(T, "1e-700"), 0);
expectEqual(try parseFloat(T, "1e+700"), std.math.inf(T));
expectEqual(@bitCast(Z, try parseFloat(T, "nAn")), @bitCast(Z, std.math.nan(T)));
expectEqual(try parseFloat(T, "inF"), std.math.inf(T));
expectEqual(try parseFloat(T, "-INF"), -std.math.inf(T));
expectEqual(try parseFloat(T, "0.4e0066999999999999999999999999999999999999999999999999999"), std.math.inf(T));
if (T != f16) {
expect(approxEq(T, try parseFloat(T, "1e-2"), 0.01, epsilon));
expect(approxEq(T, try parseFloat(T, "1234e-2"), 12.34, epsilon));
expect(approxEq(T, try parseFloat(T, "123142.1"), 123142.1, epsilon));
expect(approxEq(T, try parseFloat(T, "-123142.1124"), @as(T, -123142.1124), epsilon));
expect(approxEq(T, try parseFloat(T, "0.7062146892655368"), @as(T, 0.7062146892655368), epsilon));
}
}
}
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