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Add: PI upper/lower bound f16 constants to ScalarValue #19497

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Merged
Jefffrey merged 2 commits into from
Dec 27, 2025
Merged

Add: PI upper/lower bound f16 constants to ScalarValue #19497

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f793db3
add support for f16
xonx4l Dec 26, 2025
088b72a
typo fix
xonx4l Dec 26, 2025
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12 changes: 12 additions & 0 deletions datafusion/common/src/scalar/consts.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,24 +17,36 @@

// Constants defined for scalar construction.

// Next F16 value above π (upper bound)
pub(super) const PI_UPPER_F16: half::f16 = half::f16::from_bits(0x4249);
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@Jefffrey Jefffrey Dec 26, 2025

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How/where are these constants sourced from?

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@xonx4l xonx4l Dec 26, 2025

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These are the IEEE 754 binary16 half-precision bit representations closest to pi.

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@xonx4l xonx4l Dec 26, 2025

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I converted std::f64::consts::PI to f16 which results in 0x4248 (approx 3.1406). Since this value is slightly lower than the actual Pi. I used the next representable bit pattern (0x4249) to ensure a strict upper bound.


// Next f32 value above π (upper bound)
pub(super) const PI_UPPER_F32: f32 = std::f32::consts::PI.next_up();

// Next f64 value above π (upper bound)
pub(super) const PI_UPPER_F64: f64 = std::f64::consts::PI.next_up();

// Next f16 value below -π (lower bound)
pub(super) const NEGATIVE_PI_LOWER_F16: half::f16 = half::f16::from_bits(0xC249);

// Next f32 value below -π (lower bound)
pub(super) const NEGATIVE_PI_LOWER_F32: f32 = (-std::f32::consts::PI).next_down();

// Next f64 value below -π (lower bound)
pub(super) const NEGATIVE_PI_LOWER_F64: f64 = (-std::f64::consts::PI).next_down();

// Next f16 value above π/2 (upper bound)
pub(super) const FRAC_PI_2_UPPER_F16: half::f16 = half::f16::from_bits(0x3E49);

// Next f32 value above π/2 (upper bound)
pub(super) const FRAC_PI_2_UPPER_F32: f32 = std::f32::consts::FRAC_PI_2.next_up();

// Next f64 value above π/2 (upper bound)
pub(super) const FRAC_PI_2_UPPER_F64: f64 = std::f64::consts::FRAC_PI_2.next_up();

// Next f32 value below -π/2 (lower bound)
pub(super) const NEGATIVE_FRAC_PI_2_LOWER_F16: half::f16 = half::f16::from_bits(0xBE49);

// Next f32 value below -π/2 (lower bound)
pub(super) const NEGATIVE_FRAC_PI_2_LOWER_F32: f32 =
(-std::f32::consts::FRAC_PI_2).next_down();
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18 changes: 10 additions & 8 deletions datafusion/common/src/scalar/mod.rs
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Expand Up @@ -1342,8 +1342,7 @@ impl ScalarValue {
/// Returns a [`ScalarValue`] representing PI's upper bound
pub fn new_pi_upper(datatype: &DataType) -> Result<ScalarValue> {
match datatype {
// TODO: half::f16 doesn't seem to have equivalent
// https://github.com/apache/datafusion/issues/19465
DataType::Float16 => Ok(ScalarValue::Float16(Some(consts::PI_UPPER_F16))),
DataType::Float32 => Ok(ScalarValue::from(consts::PI_UPPER_F32)),
DataType::Float64 => Ok(ScalarValue::from(consts::PI_UPPER_F64)),
_ => {
Expand All @@ -1355,8 +1354,9 @@ impl ScalarValue {
/// Returns a [`ScalarValue`] representing -PI's lower bound
pub fn new_negative_pi_lower(datatype: &DataType) -> Result<ScalarValue> {
match datatype {
// TODO: half::f16 doesn't seem to have equivalent
// https://github.com/apache/datafusion/issues/19465
DataType::Float16 => {
Ok(ScalarValue::Float16(Some(consts::NEGATIVE_PI_LOWER_F16)))
}
DataType::Float32 => Ok(ScalarValue::from(consts::NEGATIVE_PI_LOWER_F32)),
DataType::Float64 => Ok(ScalarValue::from(consts::NEGATIVE_PI_LOWER_F64)),
_ => {
Expand All @@ -1368,8 +1368,9 @@ impl ScalarValue {
/// Returns a [`ScalarValue`] representing FRAC_PI_2's upper bound
pub fn new_frac_pi_2_upper(datatype: &DataType) -> Result<ScalarValue> {
match datatype {
// TODO: half::f16 doesn't seem to have equivalent
// https://github.com/apache/datafusion/issues/19465
DataType::Float16 => {
Ok(ScalarValue::Float16(Some(consts::FRAC_PI_2_UPPER_F16)))
}
DataType::Float32 => Ok(ScalarValue::from(consts::FRAC_PI_2_UPPER_F32)),
DataType::Float64 => Ok(ScalarValue::from(consts::FRAC_PI_2_UPPER_F64)),
_ => {
Expand All @@ -1381,8 +1382,9 @@ impl ScalarValue {
// Returns a [`ScalarValue`] representing FRAC_PI_2's lower bound
pub fn new_neg_frac_pi_2_lower(datatype: &DataType) -> Result<ScalarValue> {
match datatype {
// TODO: half::f16 doesn't seem to have equivalent
// https://github.com/apache/datafusion/issues/19465
DataType::Float16 => Ok(ScalarValue::Float16(Some(
consts::NEGATIVE_FRAC_PI_2_LOWER_F16,
))),
DataType::Float32 => {
Ok(ScalarValue::from(consts::NEGATIVE_FRAC_PI_2_LOWER_F32))
}
Expand Down