diff options
| -rw-r--r-- | library/core/src/num/flt2dec/strategy/dragon.rs | 49 |
1 files changed, 26 insertions, 23 deletions
diff --git a/library/core/src/num/flt2dec/strategy/dragon.rs b/library/core/src/num/flt2dec/strategy/dragon.rs index 751edd3c793..f8db6370653 100644 --- a/library/core/src/num/flt2dec/strategy/dragon.rs +++ b/library/core/src/num/flt2dec/strategy/dragon.rs @@ -12,48 +12,51 @@ use crate::num::flt2dec::{round_up, Decoded, MAX_SIG_DIGITS}; static POW10: [Digit; 10] = [1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000]; -static TWOPOW10: [Digit; 10] = - [2, 20, 200, 2000, 20000, 200000, 2000000, 20000000, 200000000, 2000000000]; - -// precalculated arrays of `Digit`s for 10^(2^n) -static POW10TO16: [Digit; 2] = [0x6fc10000, 0x2386f2]; -static POW10TO32: [Digit; 4] = [0, 0x85acef81, 0x2d6d415b, 0x4ee]; -static POW10TO64: [Digit; 7] = [0, 0, 0xbf6a1f01, 0x6e38ed64, 0xdaa797ed, 0xe93ff9f4, 0x184f03]; -static POW10TO128: [Digit; 14] = [ - 0, 0, 0, 0, 0x2e953e01, 0x3df9909, 0xf1538fd, 0x2374e42f, 0xd3cff5ec, 0xc404dc08, 0xbccdb0da, - 0xa6337f19, 0xe91f2603, 0x24e, +// precalculated arrays of `Digit`s for 5^(2^n). +static POW5TO16: [Digit; 2] = [0x86f26fc1, 0x23]; +static POW5TO32: [Digit; 3] = [0x85acef81, 0x2d6d415b, 0x4ee]; +static POW5TO64: [Digit; 5] = [0xbf6a1f01, 0x6e38ed64, 0xdaa797ed, 0xe93ff9f4, 0x184f03]; +static POW5TO128: [Digit; 10] = [ + 0x2e953e01, 0x3df9909, 0xf1538fd, 0x2374e42f, 0xd3cff5ec, 0xc404dc08, 0xbccdb0da, 0xa6337f19, + 0xe91f2603, 0x24e, ]; -static POW10TO256: [Digit; 27] = [ - 0, 0, 0, 0, 0, 0, 0, 0, 0x982e7c01, 0xbed3875b, 0xd8d99f72, 0x12152f87, 0x6bde50c6, 0xcf4a6e70, - 0xd595d80f, 0x26b2716e, 0xadc666b0, 0x1d153624, 0x3c42d35a, 0x63ff540e, 0xcc5573c0, 0x65f9ef17, - 0x55bc28f2, 0x80dcc7f7, 0xf46eeddc, 0x5fdcefce, 0x553f7, +static POW5TO256: [Digit; 19] = [ + 0x982e7c01, 0xbed3875b, 0xd8d99f72, 0x12152f87, 0x6bde50c6, 0xcf4a6e70, 0xd595d80f, 0x26b2716e, + 0xadc666b0, 0x1d153624, 0x3c42d35a, 0x63ff540e, 0xcc5573c0, 0x65f9ef17, 0x55bc28f2, 0x80dcc7f7, + 0xf46eeddc, 0x5fdcefce, 0x553f7, ]; #[doc(hidden)] pub fn mul_pow10(x: &mut Big, n: usize) -> &mut Big { debug_assert!(n < 512); + // Save ourself the left shift for the smallest cases. + if n < 8 { + return x.mul_small(POW10[n & 7]); + } + // Multiply by the powers of 5 and shift the 2s in at the end. + // This keeps the intermediate products smaller and faster. if n & 7 != 0 { - x.mul_small(POW10[n & 7]); + x.mul_small(POW10[n & 7] >> (n & 7)); } if n & 8 != 0 { - x.mul_small(POW10[8]); + x.mul_small(POW10[8] >> 8); } if n & 16 != 0 { - x.mul_digits(&POW10TO16); + x.mul_digits(&POW5TO16); } if n & 32 != 0 { - x.mul_digits(&POW10TO32); + x.mul_digits(&POW5TO32); } if n & 64 != 0 { - x.mul_digits(&POW10TO64); + x.mul_digits(&POW5TO64); } if n & 128 != 0 { - x.mul_digits(&POW10TO128); + x.mul_digits(&POW5TO128); } if n & 256 != 0 { - x.mul_digits(&POW10TO256); + x.mul_digits(&POW5TO256); } - x + x.mul_pow2(n) } fn div_2pow10(x: &mut Big, mut n: usize) -> &mut Big { @@ -62,7 +65,7 @@ fn div_2pow10(x: &mut Big, mut n: usize) -> &mut Big { x.div_rem_small(POW10[largest]); n -= largest; } - x.div_rem_small(TWOPOW10[n]); + x.div_rem_small(POW10[n] << 1); x } |