fpc's Introduction

Fixed-point Calculator

This program takes a range [min, max] and precision and calculates constants and information to be used in code performing calculations in this range using fixed-point integer math.

This is not an official Google product.

Try it!

$ git clone ssh://[email protected]:7999/user/fpc.git
$ make
$ ./fpc -g 30 1800 0.1
[PARAMETERS]
  min: 30 (30 requested)
  max: 1800 (1800 requested)
  precision: 0.0625 (0.1 requested)

[CODE]
  code density: 62.5%
  offset: 0
  code range: [480, 28800]

[ENCODING]
  machine bit width: 16 (15 used)
    fractional bits: 4
    integer bits: 11
  use signed: no
  machine integer type: uint16_t
  Q notation: Qu12.4

[CONVERSION]
#include <math.h>
#include <stdint.h>
// can lose precision, for display only
double convert_to_double(uint16_t x) {
  if(x < UINT16_C(480) &&
     x > UINT16_C(28800)) {
    return NAN;
  }
  return round(ldexp(x, -4) * 10) * 0.1;
}
$ make convert
$ ./convert 480 600 10000 28800
480 -> 30
600 -> 37.5
10000 -> 625
28800 -> 1800

Also, check this out:

$ ./fpc -2^7 -l-p 2^-8
[PARAMETERS]
  min: -128 (-128 requested)
  max: 127.99609375 (127.99609375 requested)
  precision: 0.00390625 (0.00390625 requested)
...

fpc has an expression evaluator built in to allow simple expressions!

supports (in order of precedence)
- parenthesis: (x)
- exponentiation: x ^ y
- multiply: x * y, divide: x / y
- addition: x + y, subtraction: x - y
some variables
- min: l
- max: h
- precision: p

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