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std.fmt.formatInt: Use an optimized path for decimals

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It enables faster decimal-to-string conversions for values in the range
[0, 100).
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Jason Phan 2022-12-05 14:58:45 -06:00 committed by GitHub
parent 9e74e4c1f8
commit 97827d6d38
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1 changed files with 38 additions and 6 deletions
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lib/std/fmt.zig
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@ -1429,12 +1429,29 @@ pub fn formatInt(
var a: MinInt = abs_value;
var index: usize = buf.len;
while (true) {
const digit = a % base;
index -= 1;
buf[index] = digitToChar(@intCast(u8, digit), case);
a /= base;
if (a == 0) break;
// TODO isComptime here because of https://github.com/ziglang/zig/issues/13335.
if (base == 10 and !isComptime()) {
while (a >= 100) : (a = @divTrunc(a, 100)) {
index -= 2;
buf[index..][0..2].* = digits2(@intCast(usize, a % 100));
}
if (a < 10) {
index -= 1;
buf[index] = '0' + @intCast(u8, a);
} else {
index -= 2;
buf[index..][0..2].* = digits2(@intCast(usize, a));
}
} else {
while (true) {
const digit = a % base;
index -= 1;
buf[index] = digitToChar(@intCast(u8, digit), case);
a /= base;
if (a == 0) break;
}
}
if (value_info.signedness == .signed) {
@ -1454,12 +1471,27 @@ pub fn formatInt(
return formatBuf(buf[index..], options, writer);
}
// TODO: Remove once https://github.com/ziglang/zig/issues/868 is resolved.
fn isComptime() bool {
var a: u8 = 0;
return @typeInfo(@TypeOf(.{a})).Struct.fields[0].is_comptime;
}
pub fn formatIntBuf(out_buf: []u8, value: anytype, base: u8, case: Case, options: FormatOptions) usize {
var fbs = std.io.fixedBufferStream(out_buf);
formatInt(value, base, case, options, fbs.writer()) catch unreachable;
return fbs.pos;
}
// Converts values in the range [0, 100) to a string.
fn digits2(value: usize) [2]u8 {
return ("0001020304050607080910111213141516171819" ++
"2021222324252627282930313233343536373839" ++
"4041424344454647484950515253545556575859" ++
"6061626364656667686970717273747576777879" ++
"8081828384858687888990919293949596979899")[value * 2 ..][0..2].*;
}
const FormatDurationData = struct {
ns: u64,
negative: bool = false,