"Illegal Function Call" Using Coprocessor in Basic 7.10 (66560)

SYMPTOMS

The following two program examples give an "Illegal Function Call" error when run as a .EXE program using a math coprocessor; however, the programs work correctly in the QBX.EXE environment or with the coprocessor disabled.

WORKAROUND

To work around this problem, do one of the following:

Break the complex equation into smaller parts that are evaluated separately. -or-
Turn off use of the coprocessor with SET NO87="message" at the MS-DOS prompt. -or-
Compile using the alternate math (/FPa) option.

STATUS

Microsoft has confirmed this to be a bug in Microsoft Basic Professional Development System (PDS) versions 7.00 and 7.10 for MS-DOS and MS OS/2. We are researching this problem and will post new information here as it becomes available.

MORE INFORMATION

Code Example 1

a = .475
b = 75
c = 62
d = .007
e = 22
f = (b * e ^ 2 / d) * SQR(1 / ((2 * b * c * a) ^ 2 + (b ^ 2 - c ^ 2))

Simplifying the equation eliminates the problem. For example, removing the (b * e ^ 2 / d) factor eliminates the error.

Code Example 2

f% = 20
q = 7
w5% = 1
ax = 1
scal = 20 * (4.666 * w5% / ax)
x1% = 95
fb = 50.967
fsd = 33
a = fb ^ 2 / fsd ^ 2
qtsd = .26
b = (a / qtsd) + (fb / (q * fsd))
vasd = 3
nd% = 1
vb = .738
c = 1 + a + (fb / (q * fsd * qtsd)) + (vasd * nd% / vb)
d = (1 / qtsd) + (fb / (q * fsd))
frq = f% / fsd
y1=frq^4 / (((frq^4 - c*frq^2 + a)^2 + (b * frq - d * frq^3)^2)^.5)

The last line in this example also gives an "illegal function call" under the same circumstances as Example 1 in this article.