mirror of
https://github.com/ashinn/chibi-scheme.git
synced 2025-05-18 21:29:19 +02:00
supporting non-native endianness and non-finite floating values
This commit is contained in:
Alex Shinn
parent
9af77c9b4f
commit
3aae0e8481
2 changed files with 175 additions and 142 deletions
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@ -9,12 +9,16 @@
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integer->bytevector bytevector->integer
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integer->hex-string hex-string->integer
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bytevector->hex-string hex-string->bytevector
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bytevector-ieee-single-ref
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bytevector-ieee-single-native-ref
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bytevector-ieee-single-set!
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bytevector-ieee-single-native-set!
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bytevector-ieee-double-ref
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bytevector-ieee-double-native-ref
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bytevector-ieee-double-set!
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bytevector-ieee-double-native-set!
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)
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(import (scheme base))
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(import (scheme base) (scheme inexact))
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(cond-expand
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(big-endian
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(begin
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@ -1,6 +1,6 @@
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;;; Copyright (c) 2004-2018 by Alex Shinn.
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;; Adapted from SRFI-56.
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;; Adapted from SRFI 56.
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; syntax
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@ -12,6 +12,22 @@
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((combine b1 b2 b3 ...)
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(combine (+ (arithmetic-shift b1 8) b2) b3 ...))))
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(define-syntax bytes-u8-set-all!
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(syntax-rules ()
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((_) bv off i)
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((_ bv off i b1) (bytevector-u8-set! bv (+ off i) b1))
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((_ bv off i b1 b2 b3 ...)
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(begin
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(bytevector-u8-set! bv (+ off i) b1)
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(bytes-u8-set-all! bv off (+ i 1) b2 b3 ...)))))
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(define-syntax bytevector-u8-set-all!
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(syntax-rules ()
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((_ bvapp iapp b1 ...)
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(let ((bv bvapp)
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(i iapp))
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(bytes-u8-set-all! bv i 0 b1 ...)))))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; reading floating point numbers
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@ -26,66 +42,71 @@
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;; http://babbage.cs.qc.edu/courses/cs341/IEEE-754references.html
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;; as references to IEEE 754.
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(define (bytevector-ieee-single-native-ref bytevector k)
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(define (mantissa expn b2 b3 b4)
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(case expn ; recognize special literal exponents
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((255)
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;;(if (zero? (combine b2 b3 b4)) +/0. 0/0.) ; XXXX for SRFI-70
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#f)
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((0) ; denormalized
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(inexact (* (expt 2.0 (- 1 (+ 127 23))) (combine b2 b3 b4))))
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(else
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(inexact
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(* (expt 2.0 (- expn (+ 127 23)))
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(combine (+ b2 128) b3 b4)))))) ; hidden bit
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(define (exponent b1 b2 b3 b4)
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(if (> b2 127) ; 1st bit of b2 is low bit of expn
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(define (bytevector-ieee-single-ref bytevector k endianness)
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(define (mantissa expn b2 b3 b4)
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(case expn
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((255) ; special exponents
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(if (zero? (combine b2 b3 b4)) (/ 1. 0.) (/ 0. 0.)))
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((0) ; denormalized
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(inexact (* (expt 2.0 (- 1 (+ 127 23))) (combine b2 b3 b4))))
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(else
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(inexact
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(* (expt 2.0 (- expn (+ 127 23)))
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(combine (+ b2 128) b3 b4)))))) ; hidden bit
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(define (exponent b1 b2 b3 b4)
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(if (> b2 127) ; 1st bit of b2 is low bit of expn
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(mantissa (+ (* 2 b1) 1) (- b2 128) b3 b4)
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(mantissa (* 2 b1) b2 b3 b4)))
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(define (sign b1 b2 b3 b4)
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(if (> b1 127) ; 1st bit of b1 is sign
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(cond ((exponent (- b1 128) b2 b3 b4) => -) (else #f))
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(define (sign b1 b2 b3 b4)
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(if (> b1 127) ; 1st bit of b1 is sign
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(- (exponent (- b1 128) b2 b3 b4))
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(exponent b1 b2 b3 b4)))
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(let* ((b1 (bytevector-u8-ref bytevector (+ k 0)))
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(b2 (bytevector-u8-ref bytevector (+ k 1)))
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(b3 (bytevector-u8-ref bytevector (+ k 2)))
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(b4 (bytevector-u8-ref bytevector (+ k 3))))
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(if (eq? (native-endianness) 'big)
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(sign b1 b2 b3 b4)
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(sign b4 b3 b2 b1))))
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(let* ((b1 (bytevector-u8-ref bytevector (+ k 0)))
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(b2 (bytevector-u8-ref bytevector (+ k 1)))
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(b3 (bytevector-u8-ref bytevector (+ k 2)))
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(b4 (bytevector-u8-ref bytevector (+ k 3))))
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(if (eq? endianness 'big)
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(sign b1 b2 b3 b4)
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(sign b4 b3 b2 b1))))
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(define (bytevector-ieee-single-native-ref bytevector k)
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(bytevector-ieee-single-ref bytevector k (native-endianness)))
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(define (bytevector-ieee-double-ref bytevector k endianness)
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(define (mantissa expn b2 b3 b4 b5 b6 b7 b8)
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(case expn
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((255) ; special exponents
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(if (zero? (combine b2 b3 b4 b5 b6 b7 b8)) (/ 1. 0.) (/ 0. 0.)))
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((0) ; denormalized
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(inexact (* (expt 2.0 (- 1 (+ 1023 52)))
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(combine b2 b3 b4 b5 b6 b7 b8))))
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(else
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(inexact
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(* (expt 2.0 (- expn (+ 1023 52)))
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(combine (+ b2 16) b3 b4 b5 b6 b7 b8)))))) ; hidden bit
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(define (exponent b1 b2 b3 b4 b5 b6 b7 b8)
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(mantissa (bitwise-ior (arithmetic-shift b1 4) ; 7 bits
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(arithmetic-shift b2 -4)) ; + 4 bits
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(bitwise-and b2 #b1111)
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b3 b4 b5 b6 b7 b8))
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(define (sign b1 b2 b3 b4 b5 b6 b7 b8)
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(if (> b1 127) ; 1st bit of b1 is sign
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(- (exponent (- b1 128) b2 b3 b4 b5 b6 b7 b8))
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(exponent b1 b2 b3 b4 b5 b6 b7 b8)))
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(let* ((b1 (bytevector-u8-ref bytevector (+ k 0)))
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(b2 (bytevector-u8-ref bytevector (+ k 1)))
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(b3 (bytevector-u8-ref bytevector (+ k 2)))
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(b4 (bytevector-u8-ref bytevector (+ k 3)))
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(b5 (bytevector-u8-ref bytevector (+ k 4)))
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(b6 (bytevector-u8-ref bytevector (+ k 5)))
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(b7 (bytevector-u8-ref bytevector (+ k 6)))
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(b8 (bytevector-u8-ref bytevector (+ k 7))))
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(if (eq? endianness 'big)
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(sign b1 b2 b3 b4 b5 b6 b7 b8)
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(sign b8 b7 b6 b5 b4 b3 b2 b1))))
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(define (bytevector-ieee-double-native-ref bytevector k)
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(define (mantissa expn b2 b3 b4 b5 b6 b7 b8)
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(case expn ; recognize special literal exponents
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((255) #f) ; won't handle NaN and +/- Inf
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((0) ; denormalized
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(inexact (* (expt 2.0 (- 1 (+ 1023 52)))
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(combine b2 b3 b4 b5 b6 b7 b8))))
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(else
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(inexact
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(* (expt 2.0 (- expn (+ 1023 52)))
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(combine (+ b2 16) b3 b4 b5 b6 b7 b8)))))) ; hidden bit
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(define (exponent b1 b2 b3 b4 b5 b6 b7 b8)
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(mantissa (bitwise-ior (arithmetic-shift b1 4) ; 7 bits
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(arithmetic-shift b2 -4)) ; + 4 bits
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(bitwise-and b2 #b1111)
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b3 b4 b5 b6 b7 b8))
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(define (sign b1 b2 b3 b4 b5 b6 b7 b8)
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(if (> b1 127) ; 1st bit of b1 is sign
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(cond ((exponent (- b1 128) b2 b3 b4 b5 b6 b7 b8) => -)
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(else #f))
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(exponent b1 b2 b3 b4 b5 b6 b7 b8)))
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(let* ((b1 (bytevector-u8-ref bytevector (+ k 0)))
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(b2 (bytevector-u8-ref bytevector (+ k 1)))
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(b3 (bytevector-u8-ref bytevector (+ k 2)))
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(b4 (bytevector-u8-ref bytevector (+ k 3)))
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(b5 (bytevector-u8-ref bytevector (+ k 4)))
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(b6 (bytevector-u8-ref bytevector (+ k 5)))
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(b7 (bytevector-u8-ref bytevector (+ k 6)))
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(b8 (bytevector-u8-ref bytevector (+ k 7))))
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(if (eq? (native-endianness) 'big)
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(sign b1 b2 b3 b4 b5 b6 b7 b8)
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(sign b8 b7 b6 b5 b4 b3 b2 b1))))
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(bytevector-ieee-double-ref bytevector k (native-endianness)))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; writing floating point numbers
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@ -104,92 +125,100 @@
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(cond
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((negative? num)
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(call-with-mantissa&exponent (- num) base mant-size exp-size proc))
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((zero? num) (proc 0 0))
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(else
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(let* ((bot (expt base mant-size))
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(top (* base bot)))
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(let loop ((n (inexact num)) (e 0))
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(cond
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((>= n top)
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(loop (/ n base) (+ e 1)))
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((< n bot)
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(loop (* n base) (- e 1)))
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(else
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(proc (exact (round n)) e))))))))
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((zero? num) (proc 0 0))
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(else
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(let* ((bot (expt base mant-size))
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(top (* base bot)))
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(let loop ((n (inexact num)) (e 0))
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(cond
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((>= n top)
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(loop (/ n base) (+ e 1)))
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((< n bot)
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(loop (* n base) (- e 1)))
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(else
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(proc (exact (round n)) e))))))))
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(define (bytevector-ieee-single-set! bytevector k num endianness)
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(define output
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(if (eq? endianness 'big)
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(lambda (b1 b2 b3 b4) (bytevector-u8-set-all! bytevector k b1 b2 b3 b4))
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(lambda (b1 b2 b3 b4) (bytevector-u8-set-all! bytevector k b4 b3 b2 b1))))
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(define (compute)
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(call-with-mantissa&exponent num 2 23 8
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(lambda (f e)
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(let ((e0 (+ e 127 23)))
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(cond
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((negative? e0)
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(let* ((f1 (exact (round (* f (expt 2 (- e0 1))))))
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(b2 (bit-field f1 16 24)) ; mant:16-23
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(b3 (bit-field f1 8 16)) ; mant:8-15
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(b4 (bit-field f1 0 8))) ; mant:0-7
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(output (if (negative? num) 128 0) b2 b3 b4)))
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((> e0 255) ; infinity
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(output (if (negative? num) 255 127) 128 0 0))
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(else
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(let* ((b0 (arithmetic-shift e0 -1))
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(b1 (if (negative? num) (+ b0 128) b0)) ; sign + exp:1-7
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(b2 (bitwise-ior
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(if (odd? e0) 128 0) ; exp:0
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(bit-field f 16 23))) ; + mant:16-23
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(b3 (bit-field f 8 16)) ; mant:8-15
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(b4 (bit-field f 0 8))) ; mant:0-7
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(output b1 b2 b3 b4))))))))
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(cond
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((zero? num) (output 0 0 0 0))
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((nan? num) (output #xff #xff #xff #xff))
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(else (compute))))
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(define (bytevector-ieee-single-native-set! bytevector k num)
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(define (bytes)
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(call-with-mantissa&exponent num 2 23 8
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(lambda (f e)
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(let ((e0 (+ e 127 23)))
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(cond
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((negative? e0)
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(let* ((f1 (exact (round (* f (expt 2 (- e0 1))))))
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(b2 (bit-field f1 16 24)) ; mant:16-23
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(b3 (bit-field f1 8 16)) ; mant:8-15
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(b4 (bit-field f1 0 8))) ; mant:0-7
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(list (if (negative? num) 128 0) b2 b3 b4)))
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((> e0 255) ; XXXX here we just write infinity
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(list (if (negative? num) 255 127) 128 0 0))
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(else
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(let* ((b0 (arithmetic-shift e0 -1))
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(b1 (if (negative? num) (+ b0 128) b0)) ; sign + exp:1-7
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(b2 (bitwise-ior
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(if (odd? e0) 128 0) ; exp:0
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(bit-field f 16 23))) ; + mant:16-23
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(b3 (bit-field f 8 16)) ; mant:8-15
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(b4 (bit-field f 0 8))) ; mant:0-7
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(list b1 b2 b3 b4))))))))
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(let ((result (cond
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((zero? num) '(0 0 0 0))
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((eq? (native-endianness) 'big) (bytes))
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(else (reverse (bytes))))))
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(bytevector-u8-set! bytevector (+ k 0) (list-ref result 0))
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(bytevector-u8-set! bytevector (+ k 1) (list-ref result 1))
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(bytevector-u8-set! bytevector (+ k 2) (list-ref result 2))
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(bytevector-u8-set! bytevector (+ k 3) (list-ref result 3))))
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(bytevector-ieee-single-set! bytevector k num (native-endianness)))
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(define (bytevector-ieee-double-set! bytevector k num endianness)
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(define output
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(if (eq? endianness 'big)
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(lambda (b1 b2 b3 b4 b5 b6 b7 b8)
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(bytevector-u8-set-all! bytevector k b1 b2 b3 b4 b5 b6 b7 b8))
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(lambda (b1 b2 b3 b4 b5 b6 b7 b8)
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(bytevector-u8-set-all! bytevector k b8 b7 b6 b5 b4 b3 b2 b1))))
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(define (compute)
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(call-with-mantissa&exponent num 2 52 11
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(lambda (f e)
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(let ((e0 (+ e 1023 52)))
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(cond
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((negative? e0)
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(let* ((f1 (exact (round (* f (expt 2 (- e0 1))))))
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(b2 (bit-field f1 48 52))
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(b3 (bit-field f1 40 48))
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(b4 (bit-field f1 32 40))
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(b5 (bit-field f1 24 32))
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(b6 (bit-field f1 16 24))
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(b7 (bit-field f1 8 16))
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(b8 (bit-field f1 0 8)))
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(output (if (negative? num) 128 0) b2 b3 b4 b5 b6 b7 b8)))
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((> e0 4095) ; infinity
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(output (if (negative? num) 255 127) 224 0 0 0 0 0 0))
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(else
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(let* ((b0 (bit-field e0 4 11))
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(b1 (if (negative? num) (+ b0 128) b0))
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(b2 (bitwise-ior (arithmetic-shift
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(bit-field e0 0 4)
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4)
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(bit-field f 48 52)))
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(b3 (bit-field f 40 48))
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(b4 (bit-field f 32 40))
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(b5 (bit-field f 24 32))
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(b6 (bit-field f 16 24))
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(b7 (bit-field f 8 16))
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(b8 (bit-field f 0 8)))
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(output b1 b2 b3 b4 b5 b6 b7 b8))))))))
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(cond
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((zero? num) (output 0 0 0 0 0 0 0 0))
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((nan? num) (output #xff #xff #xff #xff #xff #xff #xff #xff))
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(else (compute))))
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(define (bytevector-ieee-double-native-set! bytevector k num)
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(define (bytes)
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(call-with-mantissa&exponent num 2 52 11
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(lambda (f e)
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(let ((e0 (+ e 1023 52)))
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(cond
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((negative? e0)
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(let* ((f1 (exact (round (* f (expt 2 (- e0 1))))))
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(b2 (bit-field f1 48 52))
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(b3 (bit-field f1 40 48))
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(b4 (bit-field f1 32 40))
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(b5 (bit-field f1 24 32))
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(b6 (bit-field f1 16 24))
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(b7 (bit-field f1 8 16))
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(b8 (bit-field f1 0 8)))
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(list (if (negative? num) 128 0) b2 b3 b4 b5 b6 b7 b8)))
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((> e0 4095) ; infinity
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(list (if (negative? num) 255 127) 224 0 0 0 0 0 0))
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(else
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(let* ((b0 (bit-field e0 4 11))
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(b1 (if (negative? num) (+ b0 128) b0))
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(b2 (bitwise-ior (arithmetic-shift
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(bit-field e0 0 4)
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4)
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(bit-field f 48 52)))
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(b3 (bit-field f 40 48))
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(b4 (bit-field f 32 40))
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(b5 (bit-field f 24 32))
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(b6 (bit-field f 16 24))
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(b7 (bit-field f 8 16))
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(b8 (bit-field f 0 8)))
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(list b1 b2 b3 b4 b5 b6 b7 b8))))))))
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(let ((result (cond
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((zero? num) '(0 0 0 0 0 0 0 0))
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((eq? (native-endianness) 'big) (bytes))
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(else (reverse (bytes))))))
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(bytevector-u8-set! bytevector (+ k 0) (list-ref result 0))
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(bytevector-u8-set! bytevector (+ k 1) (list-ref result 1))
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(bytevector-u8-set! bytevector (+ k 2) (list-ref result 2))
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(bytevector-u8-set! bytevector (+ k 3) (list-ref result 3))
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(bytevector-u8-set! bytevector (+ k 4) (list-ref result 4))
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(bytevector-u8-set! bytevector (+ k 5) (list-ref result 5))
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(bytevector-u8-set! bytevector (+ k 6) (list-ref result 6))
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(bytevector-u8-set! bytevector (+ k 7) (list-ref result 7))))
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(bytevector-ieee-double-set! bytevector k num (native-endianness)))
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;; Local Variables:
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;; eval: (put 'call-with-mantissa&exponent 'scheme-indent-function 4)
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;; End:
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