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core/fmt: Second attempt at improving number formatting #6193

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57cb3cf
core/fmt: Adhere to the docs
BunterSchatten Jan 18, 2026
a7e3718
core/fmt: Fix tests
BunterSchatten Jan 27, 2026
b2a4856
core/fmt: Add more tests
BunterSchatten Jan 29, 2026
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308 changes: 138 additions & 170 deletions core/fmt/fmt.odin
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Original file line number Diff line number Diff line change
Expand Up @@ -1030,21 +1030,61 @@ fmt_bool :: proc(fi: ^Info, b: bool, verb: rune) {
// Inputs:
// - fi: A pointer to an Info structure
// - width: The number of padding characters to write
// - pad_byte: The padding character to write
//
fmt_write_padding :: proc(fi: ^Info, width: int) {
fmt_write_padding :: proc(fi: ^Info, width: int, pad_byte: byte) {
if width <= 0 {
return
}

pad_byte: byte = ' '
if !fi.space {
pad_byte = '0'
}

for i := 0; i < width; i += 1 {
io.write_byte(fi.writer, pad_byte, &fi.n)
}
}
// Writes the int format prefix, if any, to a buffer (for example "-0x" or " 0b")
//
// Inputs:
// - buf: The buffer to write the prefix to
// - fi: A pointer to an Info structure
// - base: The base for the integer
// - is_neg: Indicates if the number is negative and the prefix needs a "-"
//
// Returns:
// - The string containing the prefix written to the buffer
//
get_int_prefix :: proc(buf: ^[3]byte, fi: ^Info, base: int, is_neg: bool) -> string {
i := 0

if is_neg {
buf[i] = '-'
i += 1
} else if fi.plus {
buf[i] = '+'
i += 1
} else if fi.space {
buf[i] = ' '
i += 1
}

if fi.hash && base != 10 {
buf[i] = '0'
i += 1

switch base {
case 2: buf[i] = 'b'
case 8: buf[i] = 'o'
// case 10: buf[i] = 'd'
case 12: buf[i] = 'z'
case 16: buf[i] = 'x'
case:
panic("get_int_prefix: unknown base, whoops")
}

i += 1
}

return string(buf[:i])
}
// Formats an integer value with specified base, sign, bit size, and digits
//
// Inputs:
Expand All @@ -1055,77 +1095,24 @@ fmt_write_padding :: proc(fi: ^Info, width: int) {
// - bit_size: The bit size of the integer
// - digits: A string containing the digits for formatting
//
// WARNING: May panic if the width and precision are too big, causing a buffer overrun
// WARNING: May panic if the width is too big, causing a buffer overrun
//
_fmt_int :: proc(fi: ^Info, u: u64, base: int, is_signed: bool, bit_size: int, digits: string) {
_, neg := strconv.is_integer_negative(u, is_signed, bit_size)

BUF_SIZE :: 256
if fi.width_set || fi.prec_set {
width := fi.width + fi.prec + 3 // 3 extra bytes for sign and prefix
if width > BUF_SIZE {
// TODO(bill):????
panic("_fmt_int: buffer overrun. Width and precision too big")
}
if fi.width_set && fi.width > BUF_SIZE {
// TODO(bill):????
panic("_fmt_int: buffer overrun. Width too big")
}

buf: [BUF_SIZE]byte
start := 0
pre_buf: [3]byte

if fi.hash && !is_signed {
switch base {
case 2:
io.write_byte(fi.writer, '0', &fi.n)
io.write_byte(fi.writer, 'b', &fi.n)
start = 2

case 8:
io.write_byte(fi.writer, '0', &fi.n)
io.write_byte(fi.writer, 'o', &fi.n)
start = 2

case 12:
io.write_byte(fi.writer, '0', &fi.n)
io.write_byte(fi.writer, 'z', &fi.n)
start = 2

case 16:
io.write_byte(fi.writer, '0', &fi.n)
io.write_byte(fi.writer, 'x', &fi.n)
start = 2
}
}
u_abs, is_neg := strconv.is_integer_negative(u, is_signed, bit_size)
prefix := get_int_prefix(&pre_buf, fi, base, is_neg)
s := strconv.write_bits(buf[:], u_abs, base, false, bit_size, digits, {})

prec := 0
if fi.prec_set {
prec = fi.prec
if prec == 0 && u == 0 {
fmt_write_padding(fi, fi.width)
return
}
} else if fi.zero && fi.width_set {
prec = fi.width
if neg || fi.plus {
// There needs to be space for the "sign"
prec -= 1
}
}

switch base {
case 2, 8, 10, 12, 16:
break
case:
panic("_fmt_int: unknown base, whoops")
}

flags: strconv.Int_Flags
if fi.hash && !fi.zero && start == 0 { flags += {.Prefix} }
if fi.plus { flags += {.Plus} }
s := strconv.write_bits(buf[start:], u, base, is_signed, bit_size, digits, flags)
prev_zero := fi.zero
defer fi.zero = prev_zero
fi.zero = false
_pad(fi, s)
_pad(fi, prefix, s)
}
// Formats an int128 value based on the provided formatting options.
//
Expand All @@ -1140,89 +1127,21 @@ _fmt_int :: proc(fi: ^Info, u: u64, base: int, is_signed: bool, bit_size: int, d
// WARNING: Panics if the formatting options result in a buffer overrun.
//
_fmt_int_128 :: proc(fi: ^Info, u: u128, base: int, is_signed: bool, bit_size: int, digits: string) {
_, neg := strconv.is_integer_negative_128(u, is_signed, bit_size)

BUF_SIZE :: 256
if fi.width_set || fi.prec_set {
width := fi.width + fi.prec + 3 // 3 extra bytes for sign and prefix
if width > BUF_SIZE {
// TODO(bill):????
panic("_fmt_int: buffer overrun. Width and precision too big")
}
if fi.width_set && fi.width > BUF_SIZE{
// TODO(bill):????
panic("_fmt_int: buffer overrun. Width too big")
}

buf: [256]byte
start := 0

if fi.hash && !is_signed {
switch base {
case 2:
io.write_byte(fi.writer, '0', &fi.n)
io.write_byte(fi.writer, 'b', &fi.n)
start = 2

case 8:
io.write_byte(fi.writer, '0', &fi.n)
io.write_byte(fi.writer, 'o', &fi.n)
start = 2

case 12:
io.write_byte(fi.writer, '0', &fi.n)
io.write_byte(fi.writer, 'z', &fi.n)
start = 2

case 16:
io.write_byte(fi.writer, '0', &fi.n)
io.write_byte(fi.writer, 'x', &fi.n)
start = 2
}
}

prec := 0
if fi.prec_set {
prec = fi.prec
if prec == 0 && u == 0 {
fmt_write_padding(fi, fi.width)
return
}
} else if fi.zero && fi.width_set {
prec = fi.width
if neg || fi.plus {
// There needs to be space for the "sign"
prec -= 1
}
}

switch base {
case 2, 8, 10, 12, 16:
break
case:
panic("_fmt_int: unknown base, whoops")
}
pre_buf: [3]byte

flags: strconv.Int_Flags
if fi.hash && !fi.zero && start == 0 { flags += {.Prefix} }
if fi.plus { flags += {.Plus} }
s := strconv.write_bits_128(buf[start:], u, base, is_signed, bit_size, digits, flags)
u_abs, is_neg := strconv.is_integer_negative_128(u, is_signed, bit_size)
prefix := get_int_prefix(&pre_buf, fi, base, is_neg)
s := strconv.write_bits_128(buf[:], u_abs, base, false, bit_size, digits, {})

if fi.hash && fi.zero && fi.indent == 0 {
c: byte = 0
switch base {
case 2: c = 'b'
case 8: c = 'o'
case 12: c = 'z'
case 16: c = 'x'
}
if c != 0 {
io.write_byte(fi.writer, '0', &fi.n)
io.write_byte(fi.writer, c, &fi.n)
}
}

prev_zero := fi.zero
defer fi.zero = prev_zero
fi.zero = false
_pad(fi, s)
_pad(fi, prefix, s)
}
// Units of measurements:
@(rodata) __MEMORY_LOWER := " b kib mib gib tib pib eib"
Expand Down Expand Up @@ -1274,14 +1193,17 @@ _fmt_memory :: proc(fi: ^Info, u: u64, is_signed: bool, bit_size: int, units: st
copy(buf[len(str):], units[off:off+unit_len])
str = string(buf[:len(str)+unit_len])

if !fi.plus {
// Strip sign from "+<value>" but not "+Inf".
if str[0] == '+' && str[1] != 'I' {
str = str[1:]
}
prefix, s := _split_float_prefix(fi, str)

prev_zero := fi.zero
defer fi.zero = prev_zero

if str[1] == 'I' || str[0] == 'N' {
// no formatting with zero for "+Inf", "-Inf", or "NaN"
fi.zero = false
}

_pad(fi, str)
_pad(fi, prefix, s)
}
// Hex Values:
@(rodata) __DIGITS_LOWER := "0123456789abcdefx"
Expand Down Expand Up @@ -1377,29 +1299,69 @@ fmt_int_128 :: proc(fi: ^Info, u: u128, is_signed: bool, bit_size: int, verb: ru
//
// Inputs:
// - fi: A pointer to the Info struct containing formatting options.
// - prefix: prefix to write before s
// - s: The string to be padded.
//
_pad :: proc(fi: ^Info, s: string) {
_pad :: proc(fi: ^Info, prefix, s: string) {

if s == "" {
if fi.width_set {
// don't write prefix when there is no string to write
fmt_write_padding(fi, fi.width, ' ')
}
return
}

if !fi.width_set {
io.write_string(fi.writer, prefix, &fi.n)
io.write_string(fi.writer, s, &fi.n)
return
}


width := fi.width - utf8.rune_count_in_string(s)
pad_width := fi.width - utf8.rune_count_in_string(s) - utf8.rune_count_in_string(prefix)
if fi.minus { // right pad
io.write_string(fi.writer, prefix, &fi.n)
io.write_string(fi.writer, s, &fi.n)
fmt_write_padding(fi, width)
} else if !fi.space && s != "" && (s[0] == '-' || s[0] == '+') {
// left pad accounting for zero pad of negative number
io.write_byte(fi.writer, s[0], &fi.n)
fmt_write_padding(fi, width)
io.write_string(fi.writer, s[1:], &fi.n)
} else { // left pad
fmt_write_padding(fi, width)
fmt_write_padding(fi, pad_width, ' ')
} else if fi.zero {
// left pad with zero
io.write_string(fi.writer, prefix, &fi.n)
fmt_write_padding(fi, pad_width, '0')
io.write_string(fi.writer, s, &fi.n)
} else { // left pad with space
fmt_write_padding(fi, pad_width, ' ')
io.write_string(fi.writer, prefix, &fi.n)
io.write_string(fi.writer, s, &fi.n)
}
}
// Splits a float string into prefix ("+", "-", or " ") and the remaining string
//
// Inputs:
// - fi: A pointer to the Info struct containing formatting options.
// - str: the float string
//
_split_float_prefix :: proc(fi: ^Info, str: string) -> (string, string) {
prefix := ""
s_start := 0

switch str[0] {
case '+':
if fi.plus || str[1] == 'I' {
prefix = "+"
} else if fi.space {
prefix = " "
}
s_start = 1
case '-':
prefix = "-"
s_start = 1
case 'N':
if fi.plus || fi.space {
prefix = " "
}
}
return prefix, str[s_start:]
}
// Formats a floating-point number with a specific format and precision.
//
// Inputs:
Expand All @@ -1422,14 +1384,17 @@ _fmt_float_as :: proc(fi: ^Info, v: f64, bit_size: int, verb: rune, float_fmt: b
// Can return "NaN", "+Inf", "-Inf", "+<value>", "-<value>".
str := strconv.write_float(buf[:], v, float_fmt, prec, bit_size)

if !fi.plus {
// Strip sign from "+<value>" but not "+Inf".
if str[0] == '+' && str[1] != 'I' {
str = str[1:]
}
prefix, s := _split_float_prefix(fi, str)

prev_zero := fi.zero
defer fi.zero = prev_zero

if str[1] == 'I' || str[0] == 'N' {
// no formatting with zero for "+Inf", "-Inf", or "NaN"
fi.zero = false
}

_pad(fi, str)
_pad(fi, prefix, s)
}
// Formats a floating-point number with a specific format.
//
Expand Down Expand Up @@ -1629,11 +1594,14 @@ fmt_cstring16 :: proc(fi: ^Info, s: cstring16, verb: rune) {
//
fmt_pointer :: proc(fi: ^Info, p: rawptr, verb: rune) {
u := u64(uintptr(p))

prev_hash := fi.hash
defer fi.hash = prev_hash

switch verb {
case 'p', 'v', 'w':
if !fi.hash {
io.write_string(fi.writer, "0x", &fi.n)
}
// pointers have inverse behaviour for "#"
fi.hash = !fi.hash
_fmt_int(fi, u, 16, false, 8*size_of(rawptr), __DIGITS_UPPER)

case 'b': _fmt_int(fi, u, 2, false, 8*size_of(rawptr), __DIGITS_UPPER)
Expand Down
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