From 9835e2ae736235810b4ea1c162ca5e65c547e770 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sat, 18 May 2024 04:49:50 +0200 Subject: Merging upstream version 1.71.1+dfsg1. Signed-off-by: Daniel Baumann --- vendor/half/src/bfloat/convert.rs | 135 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 135 insertions(+) create mode 100644 vendor/half/src/bfloat/convert.rs (limited to 'vendor/half/src/bfloat/convert.rs') diff --git a/vendor/half/src/bfloat/convert.rs b/vendor/half/src/bfloat/convert.rs new file mode 100644 index 000000000..4aa0aec75 --- /dev/null +++ b/vendor/half/src/bfloat/convert.rs @@ -0,0 +1,135 @@ +pub(crate) fn f32_to_bf16(value: f32) -> u16 { + // Convert to raw bytes + let x = value.to_bits(); + + // check for NaN + if x & 0x7FFF_FFFFu32 > 0x7F80_0000u32 { + // Keep high part of current mantissa but also set most significiant mantissa bit + return ((x >> 16) | 0x0040u32) as u16; + } + + // round and shift + let round_bit = 0x0000_8000u32; + if (x & round_bit) != 0 && (x & (3 * round_bit - 1)) != 0 { + (x >> 16) as u16 + 1 + } else { + (x >> 16) as u16 + } +} + +pub(crate) fn f64_to_bf16(value: f64) -> u16 { + // Convert to raw bytes, truncating the last 32-bits of mantissa; that precision will always + // be lost on half-precision. + let val = value.to_bits(); + let x = (val >> 32) as u32; + + // Extract IEEE754 components + let sign = x & 0x8000_0000u32; + let exp = x & 0x7FF0_0000u32; + let man = x & 0x000F_FFFFu32; + + // Check for all exponent bits being set, which is Infinity or NaN + if exp == 0x7FF0_0000u32 { + // Set mantissa MSB for NaN (and also keep shifted mantissa bits). + // We also have to check the last 32 bits. + let nan_bit = if man == 0 && (val as u32 == 0) { + 0 + } else { + 0x0040u32 + }; + return ((sign >> 16) | 0x7F80u32 | nan_bit | (man >> 13)) as u16; + } + + // The number is normalized, start assembling half precision version + let half_sign = sign >> 16; + // Unbias the exponent, then bias for bfloat16 precision + let unbiased_exp = ((exp >> 20) as i64) - 1023; + let half_exp = unbiased_exp + 127; + + // Check for exponent overflow, return +infinity + if half_exp >= 0xFF { + return (half_sign | 0x7F80u32) as u16; + } + + // Check for underflow + if half_exp <= 0 { + // Check mantissa for what we can do + if 7 - half_exp > 21 { + // No rounding possibility, so this is a full underflow, return signed zero + return half_sign as u16; + } + // Don't forget about hidden leading mantissa bit when assembling mantissa + let man = man | 0x0010_0000u32; + let mut half_man = man >> (14 - half_exp); + // Check for rounding + let round_bit = 1 << (13 - half_exp); + if (man & round_bit) != 0 && (man & (3 * round_bit - 1)) != 0 { + half_man += 1; + } + // No exponent for subnormals + return (half_sign | half_man) as u16; + } + + // Rebias the exponent + let half_exp = (half_exp as u32) << 7; + let half_man = man >> 13; + // Check for rounding + let round_bit = 0x0000_1000u32; + if (man & round_bit) != 0 && (man & (3 * round_bit - 1)) != 0 { + // Round it + ((half_sign | half_exp | half_man) + 1) as u16 + } else { + (half_sign | half_exp | half_man) as u16 + } +} + +pub(crate) fn bf16_to_f32(i: u16) -> f32 { + // If NaN, keep current mantissa but also set most significiant mantissa bit + if i & 0x7FFFu16 > 0x7F80u16 { + f32::from_bits((i as u32 | 0x0040u32) << 16) + } else { + f32::from_bits((i as u32) << 16) + } +} + +pub(crate) fn bf16_to_f64(i: u16) -> f64 { + // Check for signed zero + if i & 0x7FFFu16 == 0 { + return f64::from_bits((i as u64) << 48); + } + + let half_sign = (i & 0x8000u16) as u64; + let half_exp = (i & 0x7F80u16) as u64; + let half_man = (i & 0x007Fu16) as u64; + + // Check for an infinity or NaN when all exponent bits set + if half_exp == 0x7F80u64 { + // Check for signed infinity if mantissa is zero + if half_man == 0 { + return f64::from_bits((half_sign << 48) | 0x7FF0_0000_0000_0000u64); + } else { + // NaN, keep current mantissa but also set most significiant mantissa bit + return f64::from_bits((half_sign << 48) | 0x7FF8_0000_0000_0000u64 | (half_man << 45)); + } + } + + // Calculate double-precision components with adjusted exponent + let sign = half_sign << 48; + // Unbias exponent + let unbiased_exp = ((half_exp as i64) >> 7) - 127; + + // Check for subnormals, which will be normalized by adjusting exponent + if half_exp == 0 { + // Calculate how much to adjust the exponent by + let e = (half_man as u16).leading_zeros() - 9; + + // Rebias and adjust exponent + let exp = ((1023 - 127 - e) as u64) << 52; + let man = (half_man << (46 + e)) & 0xF_FFFF_FFFF_FFFFu64; + return f64::from_bits(sign | exp | man); + } + // Rebias exponent for a normalized normal + let exp = ((unbiased_exp + 1023) as u64) << 52; + let man = (half_man & 0x007Fu64) << 45; + f64::from_bits(sign | exp | man) +} -- cgit v1.2.3