Thread safety

[mratsim]

Just a quick reminder that it might be necessary to use this library in a multithreaded context for example for accounting software with work split across one core per year.

In that case trivial types like arrays should be preferred over sequences if possible, for example here:

decimal128/src/decimal128/dpd.nim

Lines 72 to 127 in 9ec5431

	proc decode10bitDPD*(dpd: uint16): seq[byte] =
	# decode the 3 digits from a densley packed binary of the first 10 bits
	# returns 3 bytes containing the digits
	# original code from:
	# https://github.com/wd5gnr/DensePackDecimal/blob/master/dpd.c
	const
	FIRST_CHUNK = 0x380.uint16
	SECOND_CHUNK = 0x70.uint16
	THIRD_CHUNK = 0x7.uint16
	var x: uint16 = 0
	var y: uint16 = 0
	var z: uint16 = 0
	if nz(dpd and 8):
	if (dpd and 0xE) == 0xE:
	case (dpd and 0x60):
	of 0:
	x = 8 + ((dpd and 0x80) shr 7)
	y = 8 + ((dpd and 0x10) shr 4)
	z = ((dpd and 0x300) shr 7) or (dpd and 1)
	of 0x20:
	x = 8 + ((dpd and 0x80) shr 7)
	y = ((dpd and 0x300) shr 7) or ((dpd and 0x10) shr 4)
	z = 8 + (dpd and 1)
	of 0x40:
	x = (dpd and 0x380) shr 7
	y = 8 + ((dpd and 0x10) shr 4)
	z = 8 or (dpd and 1)
	of 0x60:
	x = 8 + ((dpd and 0x80) shr 7)
	y = 8 + ((dpd and 0x10) shr 4)
	z = 8 + (dpd and 1)
	else:
	echo "should never happen (A)"
	else:
	case (dpd and 0xE):
	of 0x8:
	x = (dpd and 0x380) shr 7
	y = (dpd and 0x70) shr 4
	z = 8 + (dpd and 1)
	of 0xA:
	x = (dpd and 0x380) shr 7
	y = 8 + ((dpd and 0x10) shr 4)
	z = ((dpd and 0x60) shr 4) or (dpd and 1)
	of 0xC:
	x = 8 + ((dpd and 0x80) shr 7)
	y = (dpd and 0x70) shr 4
	z = ((dpd and 0x300) shr 7) or (dpd and 1)
	else:
	echo "should never happen (B)"
	else:
	echo "clean"
	x = (dpd and FIRST_CHUNK) shr 7
	y = (dpd and SECOND_CHUNK) shr 4
	z = (dpd and THIRD_CHUNK)
	echo "xyz " & $x & " " & $y & " " & $z
	result = @[x.byte, y.byte, z.byte]

This also avoids memory allocation which might be a bottleneck if done regularly and which is also problematic for long-running processes as it might lead to memory fragmentation.

[JohnAD]

I will put this on my list of improvements!

That particular reference, the contents of dpd.nim are not actually being used right now as the library does not support densley packed binary yet. decimal128.nim does not even import it. But when it does, I'll be sure to convert to a static array. The array is fixed at 34 bytes, so converting to a static array will be easy.