快速回答：您有多确定将相同的输入输入到两个计算中？特别是，您引用的 C 实现说：
int mul = (1<<(bits-2));
当您进行硬编码时：
let mul: f32 = 1073741824.000000; // 1<<(bits-2)
注意 1：您已将类型mul从 an更改int为 an f32。
注意 2：在我运行程序时得到的输出中，我看到：
mul 1073741844
值得注意的是，这与您在上面编写的硬编码常量不同；它在 20 点关闭。
我通常调试这样的问题的方法，在我注意到上面的问题之前，我在这种情况下实际上是这样做的，是使用每个中间表达式的值的打印输出来检测 C 和 Rust 版本的代码，按顺序确定事情开始不同的地方，从而缩小导致“错误”的操作的范围。
在这种情况下，它涉及并行修改 C 代码和 Rust 代码，以打印出不仅包含i（或ii在 Rust 版本中）和 output的表格c，而且还打印出每个中间结果。
这是每个代码的代码，以及我最后得到的输出表。（但后来只有分析那些表，我才意识到这两个mul值不同！）
C代码：
#include <stdio.h>
#include <math.h>
#define PI 3.1415926536897932384626
#define K1 0.6072529350088812561694
int main(int argc, char **argv)
{
int i;
int bits = 32; // number of bits
int mul = (1<<(bits-2));
int n = bits; // number of elements.
int c;
printf("Cordic sin in C\n");
printf("num bits %d\n", bits);
printf("mul %d\n", mul);
printf("pi is %g\n", PI);
printf("k1 is %g\n", K1);
float shift = 2.0;
printf("computing c = atan(pow(2, -i)) * mul\n");
printf(" i \t c p a c2\n");
for(i=0;i<n;i++)
{
c = (atan(pow(2, -i)) * mul);
int neg_i = -i;
double p = pow(2, neg_i);
double a = atan(p);
int c2 = a * mul;;
printf("% 8d \t 0x%08X % 12g % 12g 0x%08X\n", i, c, p, a, c2);
}
}
锈代码：
fn generate_table () {
let pi: f32 = 3.1415926536897932384626;
let k1: f32 = 0.6072529350088812561694; // 1/k
let num_bits: uint = 32;
let num_elms: uint = num_bits;
let mul: f32 = 1073741824.000000; // 1<<(bits-2)
println!("Cordic sin in rust");
println!("num bits {}", num_bits);
println!("mul {}", mul);
println!("1 << (bits - 2): {}", (1i << (num_bits-2)) as f32);
println!("pi is {}", pi);
println!("k1 is {}", k1);
let shift: f32 = 2.0;
println!("computing c = (1f32/shift.powi(ii as i32)).atan() * mul");
println!(" i \t c p a c2\n");
for ii in range(0, num_bits) {
let ipow: f32 = 1f32/shift.powi(ii as i32);
let cur: f32 = ipow.atan() * mul;
let a = ipow.atan();
let c2 = a * mul;
//println!("table values {:.10f}", cur);
// println!("table values 0x{}", std::f32::to_str_hex(cur));
println!("{:8u} \t 0x{:8s} {:12f} {:12f} 0x{:8s}",
ii,
std::f32::to_str_hex(cur),
ipow,
a,
std::f32::to_str_hex(c2),
);
}
}
fn main() {
generate_table();
}
生成的表格：
% gcc gentable2.c && ./a.out
Cordic sin in C
num bits 32
mul 1073741824
pi is 3.14159
k1 is 0.607253
computing c = atan(pow(2, -i)) * mul
i c p a c2
0 0x3243F6A8 1 0.785398 0x3243F6A8
1 0x1DAC6705 0.5 0.463648 0x1DAC6705
2 0x0FADBAFC 0.25 0.244979 0x0FADBAFC
3 0x07F56EA6 0.125 0.124355 0x07F56EA6
4 0x03FEAB76 0.0625 0.0624188 0x03FEAB76
5 0x01FFD55B 0.03125 0.0312398 0x01FFD55B
6 0x00FFFAAA 0.015625 0.0156237 0x00FFFAAA
7 0x007FFF55 0.0078125 0.00781234 0x007FFF55
8 0x003FFFEA 0.00390625 0.00390623 0x003FFFEA
9 0x001FFFFD 0.00195312 0.00195312 0x001FFFFD
10 0x000FFFFF 0.000976562 0.000976562 0x000FFFFF
11 0x0007FFFF 0.000488281 0.000488281 0x0007FFFF
12 0x0003FFFF 0.000244141 0.000244141 0x0003FFFF
13 0x0001FFFF 0.00012207 0.00012207 0x0001FFFF
14 0x0000FFFF 6.10352e-05 6.10352e-05 0x0000FFFF
15 0x00007FFF 3.05176e-05 3.05176e-05 0x00007FFF
16 0x00003FFF 1.52588e-05 1.52588e-05 0x00003FFF
17 0x00001FFF 7.62939e-06 7.62939e-06 0x00001FFF
18 0x00000FFF 3.8147e-06 3.8147e-06 0x00000FFF
19 0x000007FF 1.90735e-06 1.90735e-06 0x000007FF
20 0x000003FF 9.53674e-07 9.53674e-07 0x000003FF
21 0x000001FF 4.76837e-07 4.76837e-07 0x000001FF
22 0x000000FF 2.38419e-07 2.38419e-07 0x000000FF
23 0x0000007F 1.19209e-07 1.19209e-07 0x0000007F
24 0x0000003F 5.96046e-08 5.96046e-08 0x0000003F
25 0x0000001F 2.98023e-08 2.98023e-08 0x0000001F
26 0x0000000F 1.49012e-08 1.49012e-08 0x0000000F
27 0x00000008 7.45058e-09 7.45058e-09 0x00000008
28 0x00000004 3.72529e-09 3.72529e-09 0x00000004
29 0x00000002 1.86265e-09 1.86265e-09 0x00000002
30 0x00000001 9.31323e-10 9.31323e-10 0x00000001
31 0x00000000 4.65661e-10 4.65661e-10 0x00000000
% rustc gentable.rs && ./gentable
gentable.rs:5:9: 5:17 warning: unused variable: `num_elms`, #[warn(unused_variables)] on by default
gentable.rs:5 let num_elms: uint = num_bits;
^~~~~~~~
Cordic sin in rust
num bits 32
mul 1073741844
1 << (bits - 2): 1073741844
pi is 3.141593
k1 is 0.607253
computing c = (1f32/shift.powi(ii as i32)).atan() * mul
i c p a c2
0 0x3243f6c0 1 0.785398 0x3243f6c0
1 0x1dac6700 0.5 0.463648 0x1dac6700
2 0xfadbb00 0.25 0.244979 0xfadbb00
3 0x7f56ea8 0.125 0.124355 0x7f56ea8
4 0x3feab78 0.0625 0.062419 0x3feab78
5 0x1ffd55c 0.03125 0.03124 0x1ffd55c
6 0xfffaab 0.015625 0.015624 0xfffaab
7 0x7fff55.8 0.007813 0.007812 0x7fff55.8
8 0x3fffea.c 0.003906 0.003906 0x3fffea.c
9 0x1ffffd.6 0.001953 0.001953 0x1ffffd.6
10 0xfffff.b 0.000977 0.000977 0xfffff.b
11 0x7ffff.f8 0.000488 0.000488 0x7ffff.f8
12 0x40000 0.000244 0.000244 0x40000
13 0x20000 0.000122 0.000122 0x20000
14 0x10000 0.000061 0.000061 0x10000
15 0x8000 0.000031 0.000031 0x8000
16 0x4000 0.000015 0.000015 0x4000
17 0x2000 0.000008 0.000008 0x2000
18 0x1000 0.000004 0.000004 0x1000
19 0x800 0.000002 0.000002 0x800
20 0x400 0.000001 0.000001 0x400
21 0x200 0 0 0x200
22 0x100 0 0 0x100
23 0x80 0 0 0x80
24 0x40 0 0 0x40
25 0x20 0 0 0x20
26 0x10 0 0 0x10
27 0x8 0 0 0x8
28 0x4 0 0 0x4
29 0x2 0 0 0x2
30 0x1 0 0 0x1
31 0x0.8 0 0 0x0.8
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