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Clean up crc module

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Use better names, remove quite a bit of dead code.
Change `><` to a name that's actually descriptive.
This commit is contained in:
Flaviu Tamas 2015-05-23 12:59:15 -04:00
commit 188bba2b3c
5 changed files with 30 additions and 76 deletions
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64
compiler/crc.nim
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@ -11,18 +11,12 @@ import
strutils
type
TCrc32* = int32
SecureHash* = int32
const
InitCrc32* = TCrc32(- 1)
InitAdler32* = int32(1)
InitCrc32 = SecureHash(- 1)
proc updateCrc32*(val: int8, crc: TCrc32): TCrc32 {.inline.}
proc updateCrc32*(val: char, crc: TCrc32): TCrc32 {.inline.}
proc crcFromBuf*(buf: pointer, length: int): TCrc32
proc strCrc32*(s: string): TCrc32
proc crcFromFile*(filename: string): TCrc32
proc updateAdler32*(adler: int32, buf: pointer, length: int): int32
proc secureHashFile*(filename: string): SecureHash
# implementation
type
@ -74,31 +68,22 @@ const
- 1000256840, 1567103746, 711928724, - 1274298825, - 1022587231, 1510334235,
755167117]
proc updateCrc32(val: int8, crc: TCrc32): TCrc32 =
result = TCrc32(crc32table[(int(crc) xor (int(val) and 0x000000FF)) and
0x000000FF]) xor (crc shr TCrc32(8))
proc updateCrc32(val: int8, crc: SecureHash): SecureHash =
result = SecureHash(crc32table[(int(crc) xor (int(val) and 0x000000FF)) and
0x000000FF]) xor (crc shr SecureHash(8))
proc updateCrc32(val: char, crc: TCrc32): TCrc32 =
proc updateCrc32(val: char, crc: SecureHash): SecureHash =
result = updateCrc32(toU8(ord(val)), crc)
proc strCrc32(s: string): TCrc32 =
proc secureHash*(s: string): SecureHash =
result = InitCrc32
for i in countup(0, len(s) - 1): result = updateCrc32(s[i], result)
proc `><`*(c: TCrc32, s: string): TCrc32 =
result = c
for i in 0..len(s)-1: result = updateCrc32(s[i], result)
type
TByteArray = array[0..10000000, int8]
PByteArray = ref TByteArray
proc crcFromBuf(buf: pointer, length: int): TCrc32 =
var p = cast[PByteArray](buf)
result = InitCrc32
for i in countup(0, length - 1): result = updateCrc32(p[i], result)
proc crcFromFile(filename: string): TCrc32 =
proc secureHashFile(filename: string): SecureHash =
const
bufSize = 8000 # don't use 8K for the memory allocator!
var
@ -114,34 +99,3 @@ proc crcFromFile(filename: string): TCrc32 =
if readBytes != bufSize: break
dealloc(buf)
close(bin)
const
base = int32(65521) # largest prime smaller than 65536
# NMAX = 5552; original code with unsigned 32 bit integer
# NMAX is the largest n
# such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1
nmax = 3854 # code with signed 32 bit integer
# NMAX is the largest n such that
# 255n(n+1)/2 + (n+1)(BASE-1) <= 2^31-1
# The penalty is the time loss in the extra MOD-calls.
proc updateAdler32(adler: int32, buf: pointer, length: int): int32 =
var
s1, s2: int32
L, k, b: int
s1 = adler and int32(0x0000FFFF)
s2 = (adler shr int32(16)) and int32(0x0000FFFF)
L = length
b = 0
while (L > 0):
if L < nmax: k = L
else: k = nmax
dec(L, k)
while (k > 0):
s1 = s1 +% int32((cast[cstring](buf))[b])
s2 = s2 +% s1
inc(b)
dec(k)
s1 = `%%`(s1, base)
s2 = `%%`(s2, base)
result = (s2 shl int32(16)) or s1