From 698f8c2f01ea549d77d7dc3338a12e04c11057b9 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:02:58 +0200 Subject: Adding upstream version 1.64.0+dfsg1. Signed-off-by: Daniel Baumann --- .../src/int/specialized_div_rem/delegate.rs | 319 +++++++++++++++++++++ 1 file changed, 319 insertions(+) create mode 100644 vendor/compiler_builtins/src/int/specialized_div_rem/delegate.rs (limited to 'vendor/compiler_builtins/src/int/specialized_div_rem/delegate.rs') diff --git a/vendor/compiler_builtins/src/int/specialized_div_rem/delegate.rs b/vendor/compiler_builtins/src/int/specialized_div_rem/delegate.rs new file mode 100644 index 000000000..330c6e4f8 --- /dev/null +++ b/vendor/compiler_builtins/src/int/specialized_div_rem/delegate.rs @@ -0,0 +1,319 @@ +/// Creates an unsigned division function that uses a combination of hardware division and +/// binary long division to divide integers larger than what hardware division by itself can do. This +/// function is intended for microarchitectures that have division hardware, but not fast enough +/// multiplication hardware for `impl_trifecta` to be faster. +#[allow(unused_macros)] +macro_rules! impl_delegate { + ( + $fn:ident, // name of the unsigned division function + $zero_div_fn:ident, // function called when division by zero is attempted + $half_normalization_shift:ident, // function for finding the normalization shift of $uX + $half_division:ident, // function for division of a $uX by a $uX + $n_h:expr, // the number of bits in $iH or $uH + $uH:ident, // unsigned integer with half the bit width of $uX + $uX:ident, // unsigned integer with half the bit width of $uD. + $uD:ident, // unsigned integer type for the inputs and outputs of `$fn` + $iD:ident // signed integer type with the same bitwidth as `$uD` + ) => { + /// Computes the quotient and remainder of `duo` divided by `div` and returns them as a + /// tuple. + pub fn $fn(duo: $uD, div: $uD) -> ($uD, $uD) { + // The two possibility algorithm, undersubtracting long division algorithm, or any kind + // of reciprocal based algorithm will not be fastest, because they involve large + // multiplications that we assume to not be fast enough relative to the divisions to + // outweigh setup times. + + // the number of bits in a $uX + let n = $n_h * 2; + + let duo_lo = duo as $uX; + let duo_hi = (duo >> n) as $uX; + let div_lo = div as $uX; + let div_hi = (div >> n) as $uX; + + match (div_lo == 0, div_hi == 0, duo_hi == 0) { + (true, true, _) => $zero_div_fn(), + (_, false, true) => { + // `duo` < `div` + return (0, duo); + } + (false, true, true) => { + // delegate to smaller division + let tmp = $half_division(duo_lo, div_lo); + return (tmp.0 as $uD, tmp.1 as $uD); + } + (false, true, false) => { + if duo_hi < div_lo { + // `quo_hi` will always be 0. This performs a binary long division algorithm + // to zero `duo_hi` followed by a half division. + + // We can calculate the normalization shift using only `$uX` size functions. + // If we calculated the normalization shift using + // `$half_normalization_shift(duo_hi, div_lo false)`, it would break the + // assumption the function has that the first argument is more than the + // second argument. If the arguments are switched, the assumption holds true + // since `duo_hi < div_lo`. + let norm_shift = $half_normalization_shift(div_lo, duo_hi, false); + let shl = if norm_shift == 0 { + // Consider what happens if the msbs of `duo_hi` and `div_lo` align with + // no shifting. The normalization shift will always return + // `norm_shift == 0` regardless of whether it is fully normalized, + // because `duo_hi < div_lo`. In that edge case, `n - norm_shift` would + // result in shift overflow down the line. For the edge case, because + // both `duo_hi < div_lo` and we are comparing all the significant bits + // of `duo_hi` and `div`, we can make `shl = n - 1`. + n - 1 + } else { + // We also cannot just use `shl = n - norm_shift - 1` in the general + // case, because when we are not in the edge case comparing all the + // significant bits, then the full `duo < div` may not be true and thus + // breaks the division algorithm. + n - norm_shift + }; + + // The 3 variable restoring division algorithm (see binary_long.rs) is ideal + // for this task, since `pow` and `quo` can be `$uX` and the delegation + // check is simple. + let mut div: $uD = div << shl; + let mut pow_lo: $uX = 1 << shl; + let mut quo_lo: $uX = 0; + let mut duo = duo; + loop { + let sub = duo.wrapping_sub(div); + if 0 <= (sub as $iD) { + duo = sub; + quo_lo |= pow_lo; + let duo_hi = (duo >> n) as $uX; + if duo_hi == 0 { + // Delegate to get the rest of the quotient. Note that the + // `div_lo` here is the original unshifted `div`. + let tmp = $half_division(duo as $uX, div_lo); + return ((quo_lo | tmp.0) as $uD, tmp.1 as $uD); + } + } + div >>= 1; + pow_lo >>= 1; + } + } else if duo_hi == div_lo { + // `quo_hi == 1`. This branch is cheap and helps with edge cases. + let tmp = $half_division(duo as $uX, div as $uX); + return ((1 << n) | (tmp.0 as $uD), tmp.1 as $uD); + } else { + // `div_lo < duo_hi` + // `rem_hi == 0` + if (div_lo >> $n_h) == 0 { + // Short division of $uD by a $uH, using $uX by $uX division + let div_0 = div_lo as $uH as $uX; + let (quo_hi, rem_3) = $half_division(duo_hi, div_0); + + let duo_mid = ((duo >> $n_h) as $uH as $uX) | (rem_3 << $n_h); + let (quo_1, rem_2) = $half_division(duo_mid, div_0); + + let duo_lo = (duo as $uH as $uX) | (rem_2 << $n_h); + let (quo_0, rem_1) = $half_division(duo_lo, div_0); + + return ( + (quo_0 as $uD) | ((quo_1 as $uD) << $n_h) | ((quo_hi as $uD) << n), + rem_1 as $uD, + ); + } + + // This is basically a short division composed of a half division for the hi + // part, specialized 3 variable binary long division in the middle, and + // another half division for the lo part. + let duo_lo = duo as $uX; + let tmp = $half_division(duo_hi, div_lo); + let quo_hi = tmp.0; + let mut duo = (duo_lo as $uD) | ((tmp.1 as $uD) << n); + // This check is required to avoid breaking the long division below. + if duo < div { + return ((quo_hi as $uD) << n, duo); + } + + // The half division handled all shift alignments down to `n`, so this + // division can continue with a shift of `n - 1`. + let mut div: $uD = div << (n - 1); + let mut pow_lo: $uX = 1 << (n - 1); + let mut quo_lo: $uX = 0; + loop { + let sub = duo.wrapping_sub(div); + if 0 <= (sub as $iD) { + duo = sub; + quo_lo |= pow_lo; + let duo_hi = (duo >> n) as $uX; + if duo_hi == 0 { + // Delegate to get the rest of the quotient. Note that the + // `div_lo` here is the original unshifted `div`. + let tmp = $half_division(duo as $uX, div_lo); + return ( + (tmp.0) as $uD | (quo_lo as $uD) | ((quo_hi as $uD) << n), + tmp.1 as $uD, + ); + } + } + div >>= 1; + pow_lo >>= 1; + } + } + } + (_, false, false) => { + // Full $uD by $uD binary long division. `quo_hi` will always be 0. + if duo < div { + return (0, duo); + } + let div_original = div; + let shl = $half_normalization_shift(duo_hi, div_hi, false); + let mut duo = duo; + let mut div: $uD = div << shl; + let mut pow_lo: $uX = 1 << shl; + let mut quo_lo: $uX = 0; + loop { + let sub = duo.wrapping_sub(div); + if 0 <= (sub as $iD) { + duo = sub; + quo_lo |= pow_lo; + if duo < div_original { + return (quo_lo as $uD, duo); + } + } + div >>= 1; + pow_lo >>= 1; + } + } + } + } + }; +} + +public_test_dep! { +/// Returns `n / d` and sets `*rem = n % d`. +/// +/// This specialization exists because: +/// - The LLVM backend for 32-bit SPARC cannot compile functions that return `(u128, u128)`, +/// so we have to use an old fashioned `&mut u128` argument to return the remainder. +/// - 64-bit SPARC does not have u64 * u64 => u128 widening multiplication, which makes the +/// delegate algorithm strategy the only reasonably fast way to perform `u128` division. +// used on SPARC +#[allow(dead_code)] +pub(crate) fn u128_divide_sparc(duo: u128, div: u128, rem: &mut u128) -> u128 { + use super::*; + let duo_lo = duo as u64; + let duo_hi = (duo >> 64) as u64; + let div_lo = div as u64; + let div_hi = (div >> 64) as u64; + + match (div_lo == 0, div_hi == 0, duo_hi == 0) { + (true, true, _) => zero_div_fn(), + (_, false, true) => { + *rem = duo; + return 0; + } + (false, true, true) => { + let tmp = u64_by_u64_div_rem(duo_lo, div_lo); + *rem = tmp.1 as u128; + return tmp.0 as u128; + } + (false, true, false) => { + if duo_hi < div_lo { + let norm_shift = u64_normalization_shift(div_lo, duo_hi, false); + let shl = if norm_shift == 0 { + 64 - 1 + } else { + 64 - norm_shift + }; + + let mut div: u128 = div << shl; + let mut pow_lo: u64 = 1 << shl; + let mut quo_lo: u64 = 0; + let mut duo = duo; + loop { + let sub = duo.wrapping_sub(div); + if 0 <= (sub as i128) { + duo = sub; + quo_lo |= pow_lo; + let duo_hi = (duo >> 64) as u64; + if duo_hi == 0 { + let tmp = u64_by_u64_div_rem(duo as u64, div_lo); + *rem = tmp.1 as u128; + return (quo_lo | tmp.0) as u128; + } + } + div >>= 1; + pow_lo >>= 1; + } + } else if duo_hi == div_lo { + let tmp = u64_by_u64_div_rem(duo as u64, div as u64); + *rem = tmp.1 as u128; + return (1 << 64) | (tmp.0 as u128); + } else { + if (div_lo >> 32) == 0 { + let div_0 = div_lo as u32 as u64; + let (quo_hi, rem_3) = u64_by_u64_div_rem(duo_hi, div_0); + + let duo_mid = ((duo >> 32) as u32 as u64) | (rem_3 << 32); + let (quo_1, rem_2) = u64_by_u64_div_rem(duo_mid, div_0); + + let duo_lo = (duo as u32 as u64) | (rem_2 << 32); + let (quo_0, rem_1) = u64_by_u64_div_rem(duo_lo, div_0); + + *rem = rem_1 as u128; + return (quo_0 as u128) | ((quo_1 as u128) << 32) | ((quo_hi as u128) << 64); + } + + let duo_lo = duo as u64; + let tmp = u64_by_u64_div_rem(duo_hi, div_lo); + let quo_hi = tmp.0; + let mut duo = (duo_lo as u128) | ((tmp.1 as u128) << 64); + if duo < div { + *rem = duo; + return (quo_hi as u128) << 64; + } + + let mut div: u128 = div << (64 - 1); + let mut pow_lo: u64 = 1 << (64 - 1); + let mut quo_lo: u64 = 0; + loop { + let sub = duo.wrapping_sub(div); + if 0 <= (sub as i128) { + duo = sub; + quo_lo |= pow_lo; + let duo_hi = (duo >> 64) as u64; + if duo_hi == 0 { + let tmp = u64_by_u64_div_rem(duo as u64, div_lo); + *rem = tmp.1 as u128; + return (tmp.0) as u128 | (quo_lo as u128) | ((quo_hi as u128) << 64); + } + } + div >>= 1; + pow_lo >>= 1; + } + } + } + (_, false, false) => { + if duo < div { + *rem = duo; + return 0; + } + let div_original = div; + let shl = u64_normalization_shift(duo_hi, div_hi, false); + let mut duo = duo; + let mut div: u128 = div << shl; + let mut pow_lo: u64 = 1 << shl; + let mut quo_lo: u64 = 0; + loop { + let sub = duo.wrapping_sub(div); + if 0 <= (sub as i128) { + duo = sub; + quo_lo |= pow_lo; + if duo < div_original { + *rem = duo; + return quo_lo as u128; + } + } + div >>= 1; + pow_lo >>= 1; + } + } + } +} +} -- cgit v1.2.3