Routines
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8A3C: Decrease the air remaining in the current cavern
 Used by the routines at 870E, 8D73 and 9028. Returns with the zero flag set if there is no air remaining. 8A3C LD A,(\$80BD) Update the game clock at 80BD 8A3F SUB \$04 8A41 LD (\$80BD),A 8A44 CP \$FC Was it just decreased from zero? 8A46 JR NZ,\$8A55 Jump if not 8A48 LD A,(\$80BC) Pick up the value of the remaining air supply from 80BC 8A4B CP \$24 Has the air supply run out? 8A4D RET Z Return (with the zero flag set) if so 8A4E DEC A Decrement the air supply at 80BC 8A4F LD (\$80BC),A 8A52 LD A,(\$80BD) Pick up the value of the game clock at 80BD 8A55 AND \$E0 A=INT(A/32); this value specifies how many pixels to draw from left to right in the cell at the right end of the air bar 8A57 RLCA 8A58 RLCA 8A59 RLCA 8A5A LD E,\$00 Initialise E to 0 (all bits reset) 8A5C OR A Do we need to draw any pixels in the cell at the right end of the air bar? 8A5D JR Z,\$8A66 Jump if not 8A5F LD B,A Copy the number of pixels to draw (1-7) to B 8A60 RRC E Set this many bits in E (from bit 7 towards bit 0) 8A62 SET 7,E 8A64 DJNZ \$8A60 8A66 LD A,(\$80BC) Pick up the value of the remaining air supply from 80BC 8A69 LD L,A Set HL to the display file address at which to draw the top row of pixels in the cell at the right end of the air bar 8A6A LD H,\$52 8A6C LD B,\$04 There are four rows of pixels to draw 8A6E LD (HL),E Draw the four rows of pixels at the right end of the air bar 8A6F INC H 8A70 DJNZ \$8A6E 8A72 XOR A Reset the zero flag to indicate that there is still some air remaining; these instructions are redundant, since the zero flag is already reset at this point 8A73 INC A 8A74 RET
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