From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sun, 4 Oct 2020 15:40:27 +0000 (+0100)
Subject: wip bigfloat Rust
X-Git-Tag: otter-0.2.0~767
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=commitdiff_plain;h=b954cf8da448a53ca598b9db2eb00b5cd13275a3;p=otter.git

wip bigfloat Rust

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---

diff --git a/src/bigfloat.rs b/src/bigfloat.rs
index d39244b6..21a40729 100644
--- a/src/bigfloat.rs
+++ b/src/bigfloat.rs
@@ -3,18 +3,72 @@
 #![allow(unused_variables)]
 #![allow(dead_code)]
 #![allow(unused_mut)]
+#![allow(unused_imports)]
+
+use crate::imports::*;
 
 enum Sign { Pos, Neg, }
 use Sign::*;
 
-struct Bigfloat {
-  sign: Sign,
-  exp: u16,
-  limbs: [[u16;3]],
+type Sz = u16;
+type Limb = [u16;3];
+
+pub struct Bigfloat(innards::Innards);
+
+mod innards {
+  use super::*;
+  use std::mem::{self, align_of, size_of};
+  use std::ptr::{self, NonNull};
+  use std::alloc::{alloc, Layout};
+
+  pub type Innards = NonNull<u8>;
+
+  struct Header {
+    sign: Sign,
+    exp: Sz,
+    nlimbs: Sz,
+  }
+
+  #[repr(C)]
+  struct Repr {
+    h: Header,
+    limbs: [Limb],
+  }
+
+  const OFFSET : usize = {
+    let h_size = size_of::<Header>();
+    let l_align = align_of::<Limb>();
+    l_align * ((h_size + l_align - 1) / l_align)
+  };
+
+  impl Bigfloat {
+    pub(in super) fn from_parts(sign: Sign, exp: Sz, limbs: &[Limb]) -> Bigfloat {
+      let nlimbs_u = limbs.len();
+      let nlimbs_sz : Sz = nlimbs_u.try_into().expect("limb count overflow");
+      let limbs_nbytes = nlimbs_u * size_of::<Limb>();
+      let all_nbytes = OFFSET + limbs_nbytes;
+      let align = max(align_of::<Header>(), align_of::<Limb>());
+      let layout = Layout::from_size_align(all_nbytes, align).unwrap();
+      unsafe {
+        let p = alloc(layout);
+        let p_header : *mut Header = mem::transmute(p);
+        let p_limbs  : *mut Limb   = mem::transmute(p.add(OFFSET));
+        ptr::write(p_header, Header { sign, exp, nlimbs: nlimbs_sz });
+        ptr::copy_nonoverlapping(limbs.as_ptr(), p_limbs, nlimbs_u);
+        Bigfloat(NonNull::new(p).unwrap())
+      }
+    }
+  }
 }
+/*/
+impl Bigfloat {
+  fn from_parts(sign: Sign, exp: Sz, limbs: &[Limb]) {
+    Bigfloat(Innards::from_parts(sign, exp, limbs))
+*/
 
 impl Bigfloat {
-  fn from_str(s: &str) -> Option<Box<Self>> {
+  #[throws(as Option)]
+  fn from_str(s: &str) -> Self {
     let mut s = s.as_bytes();
     let mut s = s.iter();
     let sign = match *s.next()? {
@@ -22,6 +76,7 @@ impl Bigfloat {
       b'!' => Neg,
       _ => None?,
     };
-    panic!();
+    let limbs = vec![];
+    Bigfloat::from_parts(sign, 0, &limbs)
   }
 }