record value in waveform_info struct returned from niscope fetch methods is wrong if record_number is non-zero

[sbethur]

Description of issue

record value in waveform_info struct returned from niscope fetch methods is wrong if record_number is non-zero. Affected public methods:

• fetch
• fetch_into
• read

System report

Command: python -c "import niscope; niscope.print_diagnostic_information()"

Output:

OS:
    Name:      Windows
    Version:   10.0.16299
    Bits:      64
Driver:
    Name:      NI-SCOPE
    Version:   20.0.0.49152
Module:
    Name:      niscope
    Version:   1.3.1
Python:
    Version:   3.6.8 (tags/v3.6.8:3c6b436a57, Dec 24 2018, 00:16:47) [MSC v.1916 64 bit (AMD64)]
    Bits:      64
    Is_Venv:   True
    Installed Packages:
        zipp==3.1.0
        toml==0.10.1
        six==1.15.0
        setuptools==49.3.1
        pytest==6.0.1
        pyparsing==2.4.7
        py==1.9.0
        pluggy==0.13.1
        pip==20.2.1
        packaging==20.4
        numpy==1.19.1
        nitclk==1.3.1
        niscope==1.3.1
        nidigital==0.9.1
        more-itertools==8.4.0
        monotonic==1.5
        iniconfig==1.0.1
        importlib-metadata==1.7.0
        hightime==0.2.0
        fasteners==0.15
        colorama==0.4.3
        attrs==19.3.0
        atomicwrites==1.4.0

Steps to reproduce issue

import nifgen
import niscope

import statistics
import time

def waveform_mean(waveforms, channel, record):
    wfm = next(wfm for wfm in waveforms if (wfm.channel == channel and wfm.record == record))
    return statistics.mean(wfm.samples)

with nifgen.Session("PXI1Slot2") as fgen_session, niscope.Session("PXI1Slot3") as scope_session:

    fgen_session.output_mode = nifgen.OutputMode.FUNC
    fgen_session.func_waveform = nifgen.Waveform.DC
    fgen_session.load_impedance = 1e6
    fgen_session.channels[0].func_dc_offset = 0.4
    fgen_session.channels[1].func_dc_offset = -0.4

    scope_session.min_sample_rate = 100e6
    scope_session.horz_num_records = 3
    scope_session.horz_min_num_pts = 1000
    scope_session.trigger_type = niscope.TriggerType.IMMEDIATE
    scope_session.channels[0,1].channel_enabled = True
    scope_session.channels[0,1].vertical_coupling = niscope.VerticalCoupling.DC
    scope_session.channels[0,1].vertical_range = 1.0
    scope_session.channels[0,1].input_impedance = 1e6

    fgen_session.initiate()
    time.sleep(1)
    scope_session.initiate()

    waveforms1 = scope_session.channels[0,1].fetch(num_samples=1000, num_records=3)
    waveforms2 = scope_session.channels[0,1].fetch(num_samples=10, offset=50, num_records=3)

for channel in ['0','1']:
    for record in [0,1,2]:
        average = waveform_mean(waveforms1, channel, record)
        print("Channel %s, Record %d average: %f" % (channel, record, average))

print()

for wfm in waveforms2:
    average = statistics.mean(wfm.samples)
    print("Channel %s, Record %d average: %f" % (wfm.channel, wfm.record, average))

# Output:
# Channel 0, Record 0 average: 0.398528
# Channel 0, Record 1 average: -0.402130
# Channel 0, Record 2 average: 0.398400
# Channel 1, Record 0 average: -0.402165
# Channel 1, Record 1 average: 0.398511
# Channel 1, Record 2 average: -0.402210
#
# Channel 0, Record 50 average: 0.397490
# Channel 0, Record 51 average: -0.402677
# Channel 0, Record 52 average: 0.398914
# Channel 1, Record 50 average: -0.401785
# Channel 1, Record 51 average: 0.399121
# Channel 1, Record 52 average: -0.401847